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University  of  California 


LABORATORY  EQUIPMENT 

FOR  PSYCHOLOGICAL 

EXPERIMENTS 


LABORATORY  EQUIPMENT 

FOR  PSYCHOLOGICAL 

EXPERIMENTS 


BY 


CHARLES  HUBBARD  JUDD,  Ph.D. 

Professor  of  Psychology  and  Director  of  the  Psychological 
Laboratory  at  Yale  University 


VOLUME  THREE 

OF  A  SERIES  OF  TEXT-BOOKS  DESIGNED  TO  INTRODUCE    THE 

STUDENT  TO  THE  METHODS  AND  PRINCIPLES 

OF  SCIENTIFIC  PSYCHOLOGY 


NEW   YORK 

CHARLES  SCRIBNER'S  SONS 

1907 


LIBRARY 


COPYRIGHT   1907  BY 

CHARLES  SCRIBNER'S  SONS 


PREFACE 

The  description  of  exercises  given  in  Volume  II  of  this 
series  was  of  set  purpose  dissociated  from  the  description 
of  apparatus,  in  view  of  the  fact  that  the  same  laboratory 
exercise  may  be  tried  with  a  very  great  variety  of  dif- 
ferent kinds  of  material  aids..  These  material  aids  can 
be  mastered  by  the  student  very  much  better  in  the  pres- 
ence of  the  apparatus  than  through  any  written  description. 
After  he  has  mastered  a  given  piece  of  apparatus  he  should 
be  called  upon  to  give  a  description  of  the  construction 
and  working  of  the  apparatus  in  his  report.  The  present 
volume  is,  accordingly,  not  designed  primarily  for  the 
student.  If  the  student  is  called  upon  to  prepare  his  own 
apparatus  as  well  as  work  out  the  exercises,  this  book 
will  be  of  advantage  to  him;  it  may  very  properly  be  used 
therefore,  by  graduate  students  who  are  preparing  to  teach 
the  subject.  Its  chief  function,  however,  will  be  in  offer- 
ing suggestions  to  those  who  wish  to  give  demonstrations 
or  to  teach  laboratory  courses. 

No  large  expenditure  of  funds  is  necessary  in  order  to 
secure  a  sufficient  equipment  with  which  to  conduct  a 
course  in  experimental  psychology.  The  apparatus  neces- 
sary for  this  course  can  with  a  few  exceptions  be  constructed 
with  the  aid  of  carpenter's  tools.  Full  lists  of  apparatus 
are  given  on  pages  243  to  249  The  Yale  Psychological 
Laboratory  is  prepared  to  supply  all  of  the  necessary 

v 

^72350 


vi  PREFACE 

pieces  of  apparatus  for  this  course  to  any  one  who  may 
wish  to  purchase  them.  Correspondence  is  invited  from 
any  who  wish  to  make  purchases,  and  a  detailed  price  list 
will  be  mailed  on  application.  If  modifications  of  designs 
furnished  are  desired,  these  modifications  will  be  intro- 
duced wherever  it  is  possible,  at  the  direction  of  the  pur- 
chaser. In  general  it  is  so  highly  desirable  that  the  equip- 
ment of  small  laboratories  for  demonstration  and  practical 
laboratory  courses  be  promoted,  that  one  of  the  important 
functions  of  the  Yale  Laboratory  in  connection  with  its 
graduate  work  is  the  provision  of  material  for  the  work 
of  its  students  and  others  of  like  interest  who  become 
teachers  of  the  subject. 

No  effort  has  been  made  in  the  following  pages  to  de- 
scribe all  of  the  different  pieces  of  apparatus  available 
for  the  various  lines  of  experimentation;  only  those  are 
described  which  are  judged  in  the  author's  experience  to 
be  serviceable  for  the  purposes  here  considered.  Fur- 
thermore, unless  apparatus  is  distinctly  the  work  of  a 
single  individual  no  effort  has  been  made  to  give  an  histori- 
cal account  of  the  way  in  which  it  has  been  designed 
and  modified  by  successive  workers.  A  practical  man- 
ual of  laboratory  equipment  is  all  that  is  aimed  at. 
Many  of  the  figures  are  copied  directly  from  the  catalogues 
of  makers  and  are  acknowledged  in  the  text  where  they 
appear.  The  other  obligations  of  the  author  to  investi- 
gators are  numerous;  many  are  acknowledged  in  the  text, 
many  require  no  special  acknowledgment  because  the 
apparatus  and  method  have  been  adopted  in  common  use. 

It  is  a  pleasure  to  make  special  acknowledgment  of 
the  contributions  of  two  gentlemen  who  make  it  their 
special  business  to  design  and  construct  psychological 
apparatus.  The  workshop  of  the  Yale  Psychological 
Laboratory  had  for  a  number  of  years  the  very  competent 


PREFACE  vii 

services  of  Mr.  Charles  Herbert  Smith.  Mr.  Smith  con- 
structed many  of  the  pieces  described  in  this  book  and  drew 
in  many  cases  the  figures.  His  successor,  Mr.  Teeuwen, 
prepared  others  of  the  drawings. 

With  the  appearance  of  this  volume  the  series  of  three 
text-books  originally  planned  is  completed.  Subsequent 
volumes  on  the  application  of  psychology  to  education 
and  cognate  subjects  are  in  preparation  and  will  be  an- 
nounced more  fully  later. 

C.  H.  J. 

New  Haven,  September,  1907. 


CONTENTS 

PAGE 

GENERAL  INTRODUCTION 1 

EXERCISE 

I.    QUANTITATIVE  STUDY  OF  GEOMETRIC     OPTICAL  ILLU- 
SIONS— 

A — Apparatus  and  Procedure .        .         16 

B— Results 22 

C — Supplementary  Experiments 24 

II.    CHARACTERISTICS  OF  THE  DIFFERENT  PARTS  OF  THE 
RETINAL  FIELD — 

A— Apparatus  and  Procedure 31 

B — Results 41 

C — Supplementary  Experiments 42 

III.  COLOR  SENSATIONS — 

A — Apparatus  and  Procedure .  . 47 

B— Results 56 

C^-Supplementary  Experiments 58 

IV.  MONOCULAR  VISUAL  EXPERIENCES — 

A  and  B — Apparatus,  Procedure,  and  Results 64 

C — Supplementary  Experiments 68 

'. V.    BINOCULAR  VISUAL  EXPERIENCES — 

A  and  B— Apparatus,  Procedure,  and  Results 78 

C — Supplementary  Experiments 87 

VI.    BINAURAL  RECOGNITION  OF  DIRECTION — 

A — Apparatus  and  Procedure 98 

B— Results. 103 

C— Supplementary  Experiments 104 

VII.    TONAL  SENSATIONS — 

A— Apparatus  and  Procedure 106 

B — Results 115 

C — Supplementary  Experiments 116 

VIII.    CUTANEOUS  SENSATIONS — 

A — Apparatus  and  Procedure 118 

C — Supplementary  Experiments 119 

ix 


[  CONTENTS 

PAGE 

IX.    TACTUAL  SPACE  PERCEPTION — 

A — Apparatus  and  Procedure 121 

B— Results 124 

C — Supplementary  Experiments 125 

X.    SENSATION  INTENSITIES — 

A — Apparatus  and  Procedure 128 

C — Supplementary  Experiments 132 

XI.    APPARATUS  AND  METHODS  FOR  RECORDING  MOVE- 
MENTS 
A — Apparatus  and  Procedure 137 

XII.    CHANGES  IN  CIRCULATION  ACCOMPANYING  CHANGES 
IN  CONSCIOUSNESS — 

A — Apparatus  and  Procedure 160 

B— Results 164 

C — Supplementary  Experiments 164 

XIII.  CHANGES  IN  MUSCULAR  TENSION  OF  THE  VOLUNTARY 

MUSCLES — 

A — Apparatus  and  Procedure 169 

B— Results 171 

C — Supplementary  Experiments 171 

XIV.  MUSCULAR  COORDINATION— 

A — Apparatus  and  Procedure 175 

B— Results 180 

C — Supplementary  Experiments 181 

XV.    UNNOTICED  VARIATIONS   IN   SIMPLE   COORDINATED 
MOVEMENTS — 

A — Apparatus  and  Procedure 182 

B— Results 196 

C — Supplementary  Experiments 196 

XVI.    VOLUNTARY  MODIFICATIONS  IN  MOVEMENT — 

A — Apparatus  and  Procedure 201 

B— Results 203 

C — Supplementary  Experiments 203 

XVII.    ANALYSIS  OF  VOLUNTARY  COORDINATIONS— 

A  and  B — Apparatus,  Procedure,  and  Results 206 

C — Supplementary  Experiments 211 


CONTENTS  xi 

PAGE 

XVIII.    EFFECTS  OF  PRACTICE  (a)  Impression  Factors 213 

C — Supplementary  Experiments 214 

XIX.    EFFECTS    OF    PRACTICE   (6)   Motor  and  Perceptual 
Habits 

A — Apparatus  and  Procedure 217 

B— Results 217 

C — Supplementary  Experiments 219 

XX.    DISTRACTION  AND  FATIGUE — 

A — Apparatus  and  Procedure 220 

B— Results 220 

C — Supplementary  Experiments 220 

XXI.    MEMORY — 

A — Apparatus  and  Procedure 224 

B— Results 227 

C — Supplementary  Experiments 228 

XXII.    FLUCTUATIONS  OF  ATTENTION — 

A — Apparatus  and  Procedure 229 

XXIII.  SCOPE  OF  ATTENTION  AND  CONSCIOUSNESS — 

A — Apparatus  and  Procedure 231 

B— Results 237 

C — Supplementary  Experiments 238 

XXIV.  ESTHETIC  APPRECIATION — 

A — Apparatus  and  Procedure 239 

B— Results 240 

C — Supplementary  Experiments 240 

XXV.    EXPERIMENTATION  WITH  COMPLEX   MENTAL  PROC- 
ESSES       242 

LISTS  OF  APPARATUS  REQUIRED  FOR  EXERCISES 243 

LIST  OF  DEMONSTRATIONS 250 

INDEX..  .  253 


LABORATORY  EQUIPMENT 

FOR  PSYCHOLOGICAL 

EXPERIMENTS 

GENERAL   INTRODUCTION 

A  PSYCHOLOGICAL  laboratory  has  two  closely  related 
functions.  It  should  be  supplied,  in  the  first  place,  with 
apparatus  that  will  make  possible  the  demonstration 
of  certain  typical  forms  of  experimental  investiga- 
tion before  the  elementary  class  which  is  pursuing  an 
introductory  course.  For  example,  if  one  is  discussing 
binocular  vision  as  a  form  of  perception  it  is  very  ad- 
vantageous that  the  members  of  the  class  should  have 
the  opportunity  of  experiencing  by  direct  observation 
some  of  the  binocular  combinations  which  can  be  made 
with  an  ordinary  hand  stereoscope.  If  the  class  is  large, 
the  apparatus  should  be  duplicated  so  that  each  member 
of  the  class  may  have  a  reasonable  opportunity  to  make 
the  observation  for  himself.  On  pages  250-252  is  given  a 
list  of  the  various  demonstrations  which  can  be  used 
with  the  author's  Psychology,  General  Introduction.  .Such 
demonstrations  as  these  pave  the  way  for  more  elaborate 
experiments  on  the  part  of  the  student. 

In  so  far  as  the  demonstrations  cover  the  same  ground 
as  the  laboratory  exercises,  which  constitute  the  second 
function  of  a  psychological  laboratory,  the  equipment 
for  demonstration  will  be  the  same  as  the  equipment 
for  the  various  individual  exercises.  There  is,  however, 
a  certain  equipment  which  is  especially  needed  for  purposes 


EQUIPMENT  FOR 

of  demonstration  and  is  not  required  for  the  laboratory 
exercises  to  be  discussed  in  detail  later.  First  among 
these  are  either  charts  or  facilities  for  lantern  projections. 
Charts  have  the  advantage  of  keeping  before  the  student 
for  a  long  time  the  outlines  which  it  is  intended  to  im- 
press upon  him.  The  best  form  of  cheap  chart  is  a  solar 
print,  such  as  is  made  by  Sprague  and  Hathaway,  36 
Bromfield  Street,  Boston,  Mass.  These  photographers 
copy  directly  any  figure  or  negative  on  charts,  which 
they  supply  for  fifty  cents  each.  The  advantage  of  a 
lantern,  on  the  other  hand,  is  that  it  is  possible  for 
any  one,  with  a  little  practice,  to  copy  from  any  book 
the  figures  which  may  be  desired  for  demonstration 
purposes.  After  meeting  the  initial  expense  of  the  lan- 
tern, the  further  acquisition  of  material  is  relatively  cheap 
as  compared  with  the  purchase  or  preparation  of  charts. 
If  possible  an  electric  arc  lantern  should  be  secured. 
A  laboratory  of  modest  equipment  can  dispense  with  any 
of  the  more  elaborate  lanterns  and  will  find  a  small  hand 
lantern  serviceable  for  many  practical  purposes  other 
than  those  of  demonstration.  Somewhat  better  than 
charts  or  lantern  slides  for  the  demonstration  of  parts 
of  the  central  nervous  system  and  the  organs  of  sense,  are 
models.  These  give  the  student  in  plastic  form  a  very 
much  better  idea  of  the  shape  and  relation  of  the  parts 
than  do  flat  drawings.  The  most  desirable  models  are 
suggested  in  the  list  on  pages  250-252. 

Special  demonstration  equipment  may  also  include  cer- 
tain large  pieces  which  are  designed  for  use  with  large 
classes.  These  special  pieces  need  not  be  discussed  here. 
For  most  laboratories  the  same  piece  will  serve  for  both 
demonstration  and  individual  experimentation. 

Turning  from  the  first  function  of  the  psychological 
laboratory  as  a  source  of  demonstrations  for  the  elementary 


PSYCHOLOGICAL  EXPERIMENTS  3 

course,  the  second  and  more  highly  specialized  function 
is  to  provide  the  material  for  individual  laboratory  exer- 
cises to  be  carried  out  by  the  students  themselves.  On 
pages  243-249  there  is  given  a  list  of  the  apparatus  with 
which  the  experimental  course  described  in  the  Labo- 
ratory Manual  can  be  conducted.  On  the  left  side  of  the 
pages  are  mentioned  those  pieces  which  are  required, 
on  the  right  those  which  are  desirable.  This  list  can  be 
indefinitely  enlarged  as  the  resources  of  the  laboratory 
permit.  On  the  other  hand,  it  can  also  be  reduced.  In 
case  the  left-hand  list  is  reduced,  it  will  be  found  that  the 
completeness  of  the  experiment  suffers.  Any  one  who 
can  not  try  the  complete  experiment  should  not  hesitate 
to  do  whatever  he  can.  The  results  may  be  very  sug- 
gestive, even  if  they  lack  something  of  the  fulness  and 
accuracy  called  for  in  the  text. 

There  are  certain  general  types  of  equipment  which  are 
not  discussed  in  connection  with  the  special  exercises. 
First,  some  equipment  for  drawing  and,  secondly,  some 
equipment  for  shop  work  are  very  desirable.  A  great  deal 
can  be  done  by  the  instructor  or  by  the  student  in  the  way 
of  preparing  simple  apparatus  for  the  laboratory  ex- 
ercises. Thus,  it  will  be  shown  in  the  description  of  the 
equipment  necessary  for  the  first  exercise  that  all  that  is 
absolutely  essential  is  a  small  number  of  cards,  a  measur- 
ing rod,  a  ruling  pen,  and  a  simple  board  tray.  The  ability 
to  draw  simple  line  figures  is  easily  acquired,  and  should 
be  cultivated  in  order  to  prepare  such  figures  as  those 
under  discussion,  and  also  in  order  to  produce  the  graphic 
representations  of  results  which  are  to  be  discussed  later. 

It  is  highly  desirable  that  there  be  in  the  psychological 
laboratory  provision  for  various  electrical  connections. 
The  greater  the  variety  of  connections  available,  the 
more  useful  will  this  equipment  be.  If  possible,  connec- 


4     LABORATORY  EQUIPMENT  FOR 

tions  should  be  secured  with  a  direct  current,  such  as  is 
used  for  incandescent  electric  lights.  In  case  such  a 
current  is  not  available,  substitutes  may  be  sought  in 
various  forms  of  battery  currents.  If  batteries  must  be 
used,  the  Edison-Lalande  batteries  are  to  be  recom- 
mended as  the  most  permanent  and  productive  in  current. 
If  the  incandescent  lighting  current  is  used,  it  will  be 
found  that  this  current  is  supplied  at  a  potential  which  is 


FlQ.  1 

From  Studies.    From  the  "  Yale  Psychological  Laboratory,"  Vol.  IV 

too  high  for  use  in  ordinary  apparatus.  A  convenient 
method  of  reducing  the  current  is  a  lamp  battery  described 
by  Professor  Scripture  and  represented  in  Fig.  1.  In 
this  battery  the  current  is  drawn  through  the  wires  E 
and  F.  Following  the  circuit  shown  in  the  diagram  at 
the  right,  we  find  that  from  F  the  current  passes  first 
through  the  lamp  at  A.  The  lamp  at  A  may  be  of 
any  desired  candle-power.  It  acts  as  a  resistance  and 


PSYCHOLOGICAL  EXPERIMENTS  5 

reduces  the  current  supplied  through  E  and  F  to  any  de- 
sired quantity.  Thus,  if  a  lamp  of  32  candle-power  is 
employed  for  A,  the  current  will  be  reduced  to  about  1 
ampere;  a  64  candle-power  lamp  gives  about  2  amperes, 
and  a  100  candle-power  lamp  gives  about  4  amperes. 
After  passing  through  the  lamp  A  the  current  may  be 
carried  along  the  path  1,  2,  and  may  either  be  turned 
through  B  or  be  carried  on  to  C.  If  carried  to  C  and  there 
drawn  off  through  wires  connected  with  the  apparatus,  the 
current  supplied  to  the  apparatus  will  be,  after  it  is  well 
established,  1  ampere.  The  current  will  then  pass  out 
through  the  series  of  connections  marked  1,  1,  1,  E. 
This  simple  connection  has  certain  marked  disadvan- 
tages, especially  at  the  moment  the  current  is  turned  off, 
when  there  is  likely  to  be  a  spark  which  may  burn  out  any 
delicate  connections.  In  order  to  take  up  the  spark,  also 
in  order  to  reduce  the  potential  of  the  current  throughout 
the  experiment,  it  is  better  to  leave  open  to  the  current 
the  second  path  B,  2,  G. 

At  B  a  small  lamp  is  inserted.  This  lamp  should  have 
an  amperage  equal  to  that  of  the  large  lamp.  For  example, 
if  the  large  lamp  A  is  32  candle-power,  the  small  lamp 
should  have  an  amperage  of  1  ampere.  The  potential 
of  the  small  lamp  may  be  relatively  small,  ranging  from 
6  to  12  volts.  If  now  with  the  connection  B,  2,  G  made, 
the  current  is  drawn  as  before  to  the  apparatus  from  the 
plug  at  C,  the  circuit  B,  2,  G,  constitutes  a  shunt,  and  any 
spark  which  is  generated  at  the  moment  the  appa- 
ratus is  disconnected  is  taken  up  by  the  shunt  circuit. 
The  shunt  circuit  will  also  act  so  as  to  reduce  the  poten- 
tial of  the  current  used  throughout  the  apparatus.  Further- 
more, the  relation  between  the  two  circuits  passing  through 
the  plugs  C  and  G  is  such  that  when  a  connection  is  made 
through  an  apparatus  of  low  resistance  at  C,  the  current 


6     LABORATORY  EQUIPMENT  FOR 

at  G  is  virtually  broken,  and,  conversely,  when  C  is  broken 
G  is  made.  This  relation  may  be  used  by  connecting 
apparatus  at  both  C  and  G;  or  a  simple  connecting  plug 
may  be  inserted  at  G,  in  which  case  the  one  source  of  sup- 
ply will  be  through  C.  The  following  table,  prepared  by 
Dr.  Scripture,  is  in  use  at  the  Yale  Laboratory: 


Mark 

Lamps  used  in  the  batteries 
LARGE  LAMPS 

on  Lamp 

Trade  Name 

A 

110  volts     100  c.  p.    4 

amperes 

B 

110  volts     100  c.  p.    3J 

amperes 

C 

110  volts      64  c.  p. 

D 

110  volts      32  c.  p. 

E 

110  volts       16  c.  p. 

F 

110  volts        8  c.  p. 

Mark 

SMALL  LAMPS 

on  Lamp 

Trade  Name 

m 

8  volts      4      amperes 

n 

8  volts      4      amperes 

0 

8  volts      4      amperes 

p 

12  volts      3      amperes 

q 

12  volts      2      amperes 

r 

12  volts       1      ampere 

s 

12  volts      0.7  ampere 

t 

10  volts      1      ampere 

u 

6  volts      1      ampere 

V 

20  volts     16      c.  p. 

Results  of  various  combinations  of  lamps. 

Lamps  used.  .  .  . 

Am    An     Ao     Bm    Bn 

Bo 

Bv 

Cm    Cn 

Potential  in  volts 

.9        5        7        7        5 

6 

37 

4        3 

Max.  cur.  in  amp.. 

.4.0    4.0    4.0    3.5    3.5 

3.5 

3.5 

1.9    1.9 

Lamps  used  .... 

.Co     Cp     Cq     Cv      Dp 

Dq 

Dr 

Dt     Du 

Potential  in  volts 

.4        7        10      25       4 

5 

11 

10       5 

Max.  cur.  in  amp. 

1.9     1.9     1.9     1.9     1.0 

1.0 

1.0 

1.0     1.0 

Lamps  used  .... 

.Dv     Eq     Er      Es       Et 

Eu 

Ev 

Fs      Fv 

Potential  in  volts. 

.  15       3        5        7        4 

2 

8 

4        6 

Max.  cur.  in  amp. 

.1.0    0.5     0.5    0.5    0.5 

0.5 

0.5 

0.3    0.3 

PSYCHOLOGICAL  EXPERIMENTS  7 

The  lamp  battery  is  relatively  uneconomical  in  its  use 
of  the  current  as  compared  with  a  transformer  through 
which  the  current  from  the  main  line  may  be  reduced  be- 
fore it  is  used  in  laboratory  apparatus.  But  a  transformer 
is  an  elaborate  piece  of  apparatus,  and  it  permits  only 
a  relatively  small  range  of  modifications  of  the  current  at 
different  points  in  the  laboratory.  The  lamp  battery  is 
portable  and  very  much  cheaper  in  initial  cost  than  the 
transformer.  It  is  capable  of  readjustments  by  changing 
the  lamps  and  yet  is  sufficiently  fixed  in  its  output  so  that 
the  student  will  not  derive  from  it  a  current  large  enough 


FIG.  2 

at  any  time  to  endanger  apparatus  by  any  mistakes  in 
connections  which  he  may  make.  For  all  these  reasons 
it  will  be  found  to  be  a  very  convenient  adjunct  to  labo- 
ratory equipment. 

The  connections  with  this  battery  and  with  the  current 
can  be  made  by  means  of  the  ordinary  screw  sockets  or  by 
means  of  contacts  of  the  following  type.  The  plug  for  this 
contact  is  represented  in  Fig.  2,  and  consists  of  a  hard  rub- 
ber block  bored  with  two  holes.  Through  these  two  holes 
pass  the  wires  D  and  E,  which  are  to  carry  the  current. 
At  one  end  of  the  hard  rubber  block  these  holes  are  en- 


s 


LABORATORY  EQUIPMENT  FOR 


larged  so  as  to  make  place  for  two  screws  A  and  B,  which 
are  set  down  into  the  hard  rubber.  These  screws  clamp 
down  the  ends  of  the  wires.  If  the  free  ends  of  the  screws 
are  split  and  the  two  parts  of  each  of  the  ends  are  spread 
slightly  apart,  they  will  spring  firmly  into  the  socket,  which 
is  represented  in  section  in  Fig.  3.  The  socket  is  just 
the  converse  of  the  plug.  It  is  made  of  hard  rubber  and 
is  bored  with  holes  for  two  wires.  These  holes  are  en- 
larged so  as  to  receive  two  metallic  cups  which  are  sup- 
plied with  screws  at  their  base  and  with  shallow  slots  at 
their  upper  end,  these  slots  being  for  a  screw-driver.  The 
cups  are  used  to  clamp  down  the  supply  wires,  and  screw 


FIG.  3 


far  enough  into  the  base  so  as  to  be  below  the  sur- 
face of  the  block.  They  are  thus  protected,  so  that  it  is 
impossible  for  anything  to  come  in  contact  with  them  ex- 
cept a  pair  of  metallic  points  which  can  be  fitted  into  the 
two  cups.  The  hard  rubber  plug  carrying  these  cups  is 
supplied  at  its  edges  with  two  extensions  by  means  of 
which  it  can  be  screwed  into  the  wall.  The  advantage 
of  such  a  plug  and  socket  as  this  is  that  the  current  can 
be  instantly  made  and  broken  without  any  screwing  or 
unscrewing  such  as  is  common  in  the  ordinary  lamp  plugs. 
A  fourth  general  type  of  equipment  which  will  be  found 
very  convenient  in  the  laboratory  consists  of  table  clamps. 


PSYCHOLOGICAL  EXPERIMENTS  9 

S-clamps,  rods,  and  holders.  A  form  of  universal  table 
clamp  which  is  very  convenient  is  represented  in  Fig.  4. 
It  consists  of  a  screw  clamp  to  be  fastened  to  the  table  and 

a  split  ball  which  is  designed  to 
carry  the  rod.  This  ball  can, 
when  undamped,  be  so  adjusted 
as  to  allow  the  rod  to  stand 
at  any  desired  angle.  When 
clamped  firmly  in  position  by 
means  of  the  screw  lever  shown 

rio.  4 

in  the  figure,  it  holds  the  rod  at 

any  position  in  which  it  has  been  set.  A  second  very  con- 
venient table  clamp  is  represented  in  Fig.  5.  The  two  jaws 
of  this  clamp  can  be  set  at  any  desired 
distance  from  each  other  along  the  rod  so 
that  they  can  be  fitted  without  difficulty 
to  any  table  or  block.  Such  a  clamp 
holds  a  rod  only  in  a  position  perpen- 
dicular to  the  table  to  which  it  is 
clamped.  The  S-clamp  or  right-angle 
clamp  is  represented  in  Fig.  6.  By 
means  of  this,  rods  of  various  sizes 
can  be  fastened  at  right  angles  to  each  FIQ 

other.    Rods  can  be  secured  either  from 
the  manufacturers  or  they  can  be  bought  in  stock  from  any 
hardware  dealer  and  can  be  cut  into  desired  lengths  by 
means  of  a  hack-saw,  which  should  be 
one  of  the  tools  in  the  workshop  of  the 
laboratory.     An  equipment  of  clamps 
and  rods  can  be  utilized  for  a  great 
variety  of  purposes.    For  example,  the 
Wheatstone  stereoscope  described  on  page  82  can  easily 
be  set  up  with  rods  and  clamps,  no  special  construction 
such  as  that  described  on  page  82  being  required. 


10          LABORATORY  EQUIPMENT  FOR 

A  general  question  of  procedure  which  may  be  discussed 
at  this  point,  rather  than  in  connection  with  any  of  the 
particular  experiments,  is  the  question  of  the  observer's 
general  attitude  toward  the  experiment.  It  will  be  found 
with  all  beginners  that  there  is  much  distraction  in  the 
conditions  under  which  the  experiment  is  made.  Further- 
more, there  is  a  natural  feeling  on  the  part  of  most  students 
that  a  psychological  experiment  is  a  test  of  their  individual 
ability  and  that  they  must,  in  order  to  do  themselves 
credit,  carry  out  the  test  with  the  greatest  degree  of  rapidity 
possible  and  with  the  highest  grade  of  attainment  in  num- 
ber of  striking  judgments.  To  a  certain  extent  this  atti- 
tude must  be  fostered,  for  the  success  of  all  psychological 
experiments  depends  upon  the  highest  possible  degree  of 
attention  which  the  observer  can  give  to  the  problem  in 
hand.  On  the  other  hand,  precautions  may  very  properly 
be  taken  in  order  to  avoid  excessive  anxiety  on  the  part 
of  the  observer,  lest  he  should  fa'il  to  comply  with  the  de- 
mands of  competition  in  the.  experiment.  It  is  better  for 
an  observer  to  recognize  that  regularity  of  reaction  or  of 
judgment  indicates  a  higher  type  of  efficiency  than  a  few 
very  rapid  and  accurate  judgments  in  the  midst  of  a 
general  series  which  is  uneven  in  its  average.  Above  all 
things  the  observer  should  free  himself  from  the  dis- 
position to  adhere  to  any  preformed  theory  of  what  the 
results  of  the  experiment  should  be.  Some  experimenters 
have  believed  that  the  best  way  to  avoid  preconceptions 
on  the  part  of  their  observers  is  to  keep  them  wholly  igno- 
rant of  the  subject  of  the  experiment  and  also  of  their  own 
results.  There  can  be  no  question  that  under  certain 
circumstances  it  is  highly  desirable  that  the  observer 
should  not  be  confused  by  a  knowledge  of  the  results.  For 
example,  in  most  practice  series  it  is  better  that  the  ob- 
server should  give  himself  wholly  to  the  task  of  practice 


PSYCHOLOGICAL  EXPERIMENTS          11 

rather  than  that  he  should  have  his  attention  divided 
between  practice  and  thought  about  how  rapidly  or  how 
slowly  he  is  progressing.  In  other  cases,  however,  it  is 
better  to  give  the  observer  definite  information,  at  least  as 
to  the  general  direction  in  which  the  experiment  is  tending. 

For  example,  in  the  experiments  on  sensation  inten- 
sities, especially  in  the  determination  of  initial  thresholds 
(see  page  128),  it  is  very  commonly  advantageous  to  tell 
the  observer  the  direction  in  which  variations  are  being 
undertaken.  If  this  is  not  done,  the  condition  should,  so 
far  as  possible,  be  arranged,  as  indicated  under  the  de- 
scription of  the  method  of  right  and  wrong  cases,  so  as 
to  take  advantage  of  the  chances  which  result  when  the 
observer  makes  a  blind  guess.  The  observer's  attitude, 
it  will  be  seen  from  this  discussion,  is  always  a  factor  in  a 
psychological  experiment. 

No  rigid  rule  can  be  laid  down  for  the  treatment  of 
the  observer.  He  will  improve  during  his  contact  with 
psychological  problems  whatever  procedure  is  followed; 
and  he  will  ultimately  find  that  a  wholly  unbiased  opinion 
is  the  most  productive  for  the  investigation.  But  these 
matters  of  attitude  can  be  cultivated  only  with  experience, 
they  can  not  be  forced  upon  the  observer  at  the  outset. 
The  more  experience  an  observer  can  have  with  regard 
to  a  problem  and  its  methods  before  he  begins  the  in- 
vestigation, the  more  rapidly  he  will  become  a  mature 
observer.  Procedure  with  knowledge,  as  it  is  technically 
called,  is  in  general  more  advantageous  than  procedure 
without,  except  as  indicated  above,  where  the  problem 
under  consideration  is  one  of  practice  and  does  not  in- 
volve any  knowledge  on  the  part  of  the  observer  of  the 
degree  or  direction  of  his  change  through  practice. 

In  this  connection  it  may  be  well  to  point  out  that  the 
results  obtained  by  beginners  are  very  frequently  so  in- 


12          LABORATORY  EQUIPMENT  FOR 

coherent  and  different  from  the  general  results  reported 
in  the  papers  of  trained  experimenters  that  the  instructor 
must  constantly  supplement  the  student's  results  by  ad- 
ditional information  or  references  for  reading,  in  order 
to  make  the  work  productive.  If  the  student  obtains  re- 
sults which  will  justify  only  a  very  broad  general  conclusion, 
there  should  be  no  effort  to  force  upon  these  vague  results 
any  greater  refinement  than  they  readily  justify.  It 
should  be  explained  to  the  student  that  the  results  which 
he  finds  reported  in  the  more  elaborate  investigations  are 
the  outcome  not  only  of  the  method  which  he  is  pursuing 
but  of  a  higher  degree  of  training  in  observation  and  re- 
action. He  should  be  encouraged  to  recognize  indi- 
vidual differences  as  important  matters  in  all  psychologi- 
cal investigations.  He  should  be  encouraged  in  con- 
nection with  each  experiment  to  give  as  full  an  account 
as  possible  of  his  own  subjective  condition.  This  will 
in  many  cases  throw  light  upon  the  character  of  the  re- 
sults which  he  obtains.  Further  discussion  of  the  matter 
of  exactness  of  psychological  results,  especially  in  so  far 
as  quantitative  methods  are  in  question,  has  been  under- 
taken in  the  general  introduction  of  the  Laboratory  Manual. 
When  the  student  has  obtained  his  results,  the  next 
matter  is  the  presentation  of  these  results.  In  general 
it  will  be  found  advantageous  to  bring  together  all  the 
results  of  an  investigation  whenever  possible  in  a  graphic 
representation.  A  graphic  representation  has  the  ad- 
vantage over  a  table  that  it  presents  at  a  single  glance 
the  whole  series  of  results  in  their  relations.  The  student 
should  be  made  familiar  with  the  use  of  coordinate 
paper  and  with  the  principles  of  reduction  to  various 
scales.  For  example,  the  following  table  was  secured  by 
an  investigator  who  carried  out  a  practice  series  of  measure- 
ments with  the  Miiller-Lyer  illusion  until  the  illusion  was 


PSYCHOLOGICAL  EXPERIMENTS 


13 


much  weakened.     This  table  was  brought  together  in  the 
curve  represented  in  Fig.  7. 


FIG.  7 


Figure  10  cm.  in  length,  oblique  3  cm.,  at  angle  of  45°. 


Date 

Avg.  111. 
in  m.m. 

M.V. 

Date 

Avg.  111. 
in  m.m. 

M.V. 

April  26 
29 

17.3 
12.3 

2.3 
2.0 

May  27 
June    1 

7.9 

8.7 

.2 
.4 

May     2 
3 

15.0 
15.9 

1.6 
1.6 

6 
6 

7.5 
6.9 

.8 
.4 

5 

17.9 

1.6 

7 

7.3 

.8 

10 

15.1 

1.0 

8 

6.8 

.3 

12 

15.0 

1.9 

10 

6.5 

.0 

17 

11.8 

1.0 

13 

4.4 

.1 

18 

12.6 

1.6 

14 

3.6 

.2 

20 

9.0 

1.2 

15 

2.5 

.9 

24 

8.2 

1.3 

16 

2.4 

.2 

25 

8.5 

1.2 

17 

1.7 

.1 

The  table  contains  the  material  which  is  expressed  in 
the  curve,  but  it  is  obvious  that  the  comprehension  of  the 
whole  matter  is  made  very  much  simpler  by  the  graphic 
representation.  Students  should  be  encouraged  to  pre- 
pare compact  tables  and  then  devise  various  methods  of 


14 


LABORATORY  EQUIPMENT  FOR 


presenting  these  tables  in  curves.  Attention  should  be 
called  to  the  fact  that  the  size  of  the  figure  is  a  matter  of 
total  indifference,  provided  the  units  of  measurements  in 
the  horizontal  are  all  of  exactly  the  same  kind  and  that 
the  units  of  measurement  in  the  vertical  are  in  turn  homo- 
geneous. It  is  sometimes  advantageous  to  emphasize  one 
characteristic  or  the  other  of  a  given  curve.  In  that  case 
small  units  may  be  used  for  the  horizontals  and  larger 
units  for  the  verticals.  Thus,  the  same  table  as  that  pre- 
sented in  Fig.  7  is  condensed  in  its  horizontal  dimensions  in 


.  8 


Fig.  8.  In  the  author's  Psychology,  General  Introdujction, 
graphic  representations  of  this  type  will  be  found  on  pages 
340,  372,  and  373. 

The  most  convenient  unit  of  space  measurement  for 
all  laboratory  exercises  is  the  centimeter  and  its  multi- 
ples and  subdivisions.  The  student  should  be  made  ac- 
quainted as  soon  as  possible  with  these  units,  and  meter 
rods  should  be  provided  in  the  general  equipment  of  the 
laboratory.  It  is  sometimes  desirable  to  provide  the  stu- 
dent with  measures  of  the  metric  system  for  his  use 
outside  of  the  laboratory.  Millimeter  coordinate  paper 


PSYCHOLOGICAL  EXPERIMENTS          15 

may  be  purchased  and  may  be  cut  into  small  strips,  if  it 
is  desired  to  attain  this  end  at  very  small  expense.  This 
paper  is  ruled  with  a  sufficient  degree  of  accuracy  to  be 
used  for  most  of  the  measurements  necessary  in  a  psy- 
chological laboratory.  All  circular  measurements  can 
be  very  much  simplified  if  apparatus  is  constructed  with 
such  a  diameter  that  a  degree  of  arc  is  exactly  equal  in 
length  to  some  one  of  the  metric  units.  If  the  diameter 
of  the  circle  is  taken  as  114.5  cm.  a  degree  of  arc  will  be 
very  nearly  equal  to  one  centimeter.  If  this  rule  of  con- 
struction in  all  circles  is  adhered  to,  the  graduation  and 
regraduation  of  the  circumference  of  these  circles  will  be 
a  very  simple  matter,  for  degrees  can  be  marked  off  on  the 
circle  with  the  aid  of  a  flexible  metric  tape. 


EXERCISE  I 

A — APPARATUS   AND   PROCEDURE 

The  form  of  figure  to  be  used  in  this  exercise  is  repre- 
sented in  the  text  of  the  Laboratory  Manual  on  page  18. 
Some  description  is  there  given  of  the  methods  to  be  em- 
ployed in  the  preparation  of  the  cards  on  which  the 
figures  are  drawn.  These  cards  should  be  large  enough 
so  that  the  boundaries  of  the  cards  shall  not  interfere  with 
the  inspection  of  the  figure.  A  convenient  size  will  be 
found  to  be  30  cm.  by  15  cm.  Any  thin  grade  of  card- 
board can  be  used,  or  a  heavy  grade  of  drawing  paper  will 
serve  very  well.  The  most  convenient  dimensions  for  the 
figures  themselves  are  10  cm.  in  length  for  Fig.  A  (Labor- 
atory Manual,  p.  18);  3  cm.  more  or  less,  as  suggested  in 
the  table  of  variations  below,  for  the  oblique  lines;  and 
angles  from  15  to  75  degrees  between  the  obliques  and 
the  long  lines.  The  line  B  (Laboratory  Manual,  p.  18) 
should  be  drawn  about  16  cm.  in  length,  and  its  obliques 
should  correspond  to  the  obliques  for  Fig.  A.  A  conven- 
ient method  of  describing  these  figures  for  purposes  of 
record  is  by  means  of  some  such  formula  as  the  follow- 
ing: 10  cm.,  3  cm.,  45°. 

The  following  variations  may  be  suggested: 


10  cm. 


10  cm.,  3  cm. 


15° 
30° 
45° 
60° 
75° 


Each  member  of  the  class  should  be  required  in  some 

16 


PSYCHOLOGICAL  EXPERIMENTS          17 

part  of  the  exercise  to  work  with  figure  10  cm.,  3  cm.,  45°. 
There  will  then  be  a  basis  for  comparison  of  all  observers. 

Modifications  of  a  different  kind  from  those  suggested 
in  the  tables  may  be  introduced  by  omitting  certain  of 
the  oblique  lines,  in  order  to  ascertain,  for  example, 
whether  an  upper  oblique  is  more  important  for  the 
illusion  than  the  corresponding  lower  oblique.  The 
length  of  the  main  line  of  the  illusion  may  also  be  modi- 
fied. In  that  case  the  comparison  between  different 
figures  should  be  made,  not  by  direct  comparison  of  the 
absolute  amount  of  the  illusion,  but  rather  in  percentages. 
Thus,  if  the  illusion  for  10  cm.,  amounts  to  2  cm.,  the 
illusion  will  be  stated  as  20%.  If  the  illusion  when  A  is 
5  cm.  in  length  amounts  to  10  mm.  it  should  again  be 
stated  at  20%.  Further  variations  may  be  introduced 
into  the  figure  by  moving  the  whole  figure  to  a  greater 
or  less  distance  from  the  observer;  this  reduces  the  size 
of  the  retinal  image  while  maintaining  a  proportional  re- 
lation between  all  of  the  different  parts.  Again,  the 
figure  may  be  turned  so  that  its  long  lines  are  vertical  or 
oblique. 

A  convenient  method  of  preparing  these  cards  in  such 
a  way  that  the  long  lines  can  easily  be  matched  with  each 
other,  is  to  set  the  cards  against  a  straight  edge  and 
draw  the  long  lines  on  both  with  one  continuous  ruling. 
In  the  same  way,  the  easiest  method  of  manipulating  the 
cards  is  to  place  them  in  some  form  of  tray  or  holder 
which  has  at  one  edge  a  straight  strip.  For  this  purpose 
a  simple  apparatus  can  be  used  consisting  of  a  board 
that  has  tacked  along  one  side  a  strip  of  wood  which 
rises  above  the  level  of  the  board  and  gives  an  edge  against 
which  to  rest  the  cards.  This  wooden  tray  can  then  be 
held  before  the  observer,  either  in  the  hand  or  resting 
upon  a  table. 


18 


LABORATORY  EQUIPMENT  FOR 


The  procedure  of  the  experiment  is  now  very  simple 
as  stated  in  the  Manual.  The  observer  should  move  the 
card  on  which  is  drawn  figure  A  until  the  length  of  the 
line  B  seems  to  him  to  be  equal  to  the  line  A.  After  he 
has  adjusted  the  cards  so  that  they  are  satisfactory,  one 
of  two  methods  may  be  adopted  for  the  measurement  of 
the  results.  First,  two  persons  may  work  together  on 
the  exercise,  one  acting  as  observer  and  the  other  acting 
as  experimenter,  and  measuring  the  results  immediately 
after  each  setting.  Secondly,  the  observer  may  mark  off 


"         F 


FIG.  9 

on  strips  of  paper  the  length  of  B  after  each  setting,  and 
may  then  measure  the  marked  strip  after  the  whole  series 
is  finished.  If  the  observer  is  allowed  to  measure  the  line 
B  after  each  setting,  he  is  likely  to  be  more  or  less  dis- 
tracted by  his  knowledge  of  the  inequality  between  A 
and  B. 

The  apparatus  for  holding  the  cards  and  recording 
measurements  may  be  made  much  more  elaborate,  as 
indicated  in  Fig.  9.  A  wooden  frame  50  cm.  long  and 


PSYCHOLOGICAL  EXPERIMENTS          19 

30  cm.  wide  is  made  up  of  a  wide  board  AA  and  a  narrow 
board  BB,  held  together  by  two  side  pieces  shown  in  the 
figure.  Between  AA  and  BB  slides  the  movable  piece  of 
board  CC.  This  is  matched  to  the  two  parts  of  the  frame 
AA  and  BB,  and  is  made  loose  enough  to  slide  freely. 
It  is  held  in  position  by  a  long,  slightly  bent  strip  of  brass 
which  acts  as  a  spring  and  is  placed  between  the  upper 
edge  of  CC  and  the  lower  edge  of  BB.  This  spring  will 
be  found  convenient  in  all  types  of  wooden  slides.  It 
obviates  the  necessity  of  fitting  the  wood  closely  and  frees 
the  apparatus  from  all  the  effects  of  swelling  through 
changes  in  humidity.  Cards  with  the  figure  to  be  meas- 
ured can  now  be  fastened  with  thumb  tacks  upon  AA 
and  CC.  The  card  EE  will  in  this  case  need  to  be  some- 
what wider  than  described  above.  The  advantage  of 
the  apparatus  as  thus  far  described  is  that  the  cards  when 
once  adjusted  are  held  in  position  and  can  be  rapidly 
adjusted  without  direct  handling.  Measurements  which 
give  no  direct  knowledge  of  the  error  can  be  made  by  the 
observer  after  each  setting  by  measuring  the  amount  by 
which  C  projects  to  the  right  beyond  the  frame. 

The  remaining  parts  of  the  apparatus  represented  in 
Fig.  9  provide  a  means  for  recording  the  settings  without 
direct  measurement.  At  the  extreme  left  of  the  figure  is 
an  arm  on  which  is  placed  a  spool  of  ticker  tape.  This  is 
unwound,  as  shown  in  T,  T,  T,  T,  and  drawn  across  the 
upper  part  of  the  frame  BB.  Two  strips  of  metal  seen 
near  the  ends  of  BB  hold  the  tape  in  place.  At  the  mid- 
dle of  BB,  and  CC,  are  placed  the  recording  points.  The 
recording  apparatus  is  constructed  as  follows :  F  is  a  short 
metal  rod  fastened  to  the  sliding  board  CC  and  seen  in 
the  figure  only  at  its  end.  The  end  of  this  rod  F  which  is 
nearest  to  the  ticker  tape  carries  a  small  pin-point.  The 
pin-point  is  held  away  from  the  paper  by  a  coil  spring 


20          LABORATORY  EQUIPMENT  FOR 

placed  around  the  rod.  (For  the  details  of  such  a  spring 
see  Fig.  18,  page  29.)  The  observer,  when  he  desires, 
can  push  against  the  upper  end  of  the  rod  F,  and  thus 
drive  the  pin  through  the  ticker  tape,  otherwise  the  pin 
is  drawn  back  by  the  spring  and  the  whole  moves  freely 
across  the  tape  whenever  the  sliding  board  CC  is  moved. 
A  second  pin-point  at  G  is  fastened  to  a  plate  H ,  which  is 
fastened  in  turn  to  BB.  The  pin-point  at  G  is  made 
double,  so  that  its  impression  may  easily  be  distinguished 
from  the  impressions  of  the  point  F.  The  plate  H  and 
the  points  at  G  are  held  away  from  the  ticker  tape  by  a 
spring.  Pressure  on  the  plate  may,  however,  as  in  the 
case  of  the  point  of  F,  drive  the  pins  at  G  into  the  tape. 
By  means  of  a  catch  placed  on  F,  a  single  pressure  on  F 
moves  both  F  and  the  plate  //  downward  to  the  tape 
against  their  respective  springs,  and  there  will  thus  be 
punctured  in  the  tape  two  pin-records,  one  at  G  and  one 
at  F.  Since  G  is  fixed  and  F  moves  as  the  board  CC  moves, 
the  distance  between  the  pinholes  in  the  tape  will  vary 
with  every  change  in  the  positions  of  the  two  cards  DD 
and  EE.  If  the  distance  between  the  pins  in  G  and 
F  is  determined  when  A  and  B  are  in  reality  equal,  the 
amount  of  departure  from  this  distance  in  the  various 
settings  will  constitute  a  measure  of  the  illusion.  The 
advantage  of  this  apparatus  is  that  the  observer  can  make 
a  series  of  settings  of  the  figure  in  rapid  succession,  and 
can  readily  record  the  results  without  the  inconvenience 
of  marking  on  strips  of  paper. 

A  further  refinement  of  the  apparatus  consists  in  at- 
taching to  the  sliding  board  CC  a  handle  which  will  per- 
mit rapid  coarse  adjustments  and  slower  fine  adjustments. 
Such  a  handle  is  represented  in  Fig.  10.  Let  B  represent 
the  end  of  the  board  CC.  The  block  K  attached  to  B 
carries  a  screw  rod  D.  The  method  of  setting  this  rod 


PSYCHOLOGICAL  EXPERIMENTS 


21 


into  the  block  K  is  such  that  it  shall  have  a  screw  move- 
ment and  at  the  same  time  a  hinge  movement  from  D 
to  D'.  The  upper  end  of  the  rod  is  turned  so  as  to 
have  a  ball-shaped  head  carried  on  a  shaft  which  is 
turned  down  to  a  diameter  smaller  than  that  of  the  ball 
or  rod.  This  head  is  fitted  into  a  cup  which  closes  around 
it  on  all  sides  except  one,  where  it  is  split  so  as  to  allow 
the  narrow  part  of  the  shaft  to  swing  forward  into  the 
position  D'  without  drawing  the  shaft  out  of  the  cup. 
The  bent  brass  strip  at  S  acts  as  a  spring  to  throw  the  rod 
into  the  position  D  against  N.  N  is  a  half 
nut  and  is  fastened  to  the  frame  of  the  ap- 
paratus. When  the  screw  rod  D  is  forced 
into  this  nut,  the  board  B  can  be  moved 
only  by  turning  the  rod  and  thus  operating 
the  screw  in  the  nut.  If  the  rod  is  drawn 
forward  into  the  position  Z)',  the  threads 
of  the  screw  no  longer  engage  the  threads 
of  the  nut  and  the  board  B  may  be  pushed 
freely  back  and  forth.  This  makes  possible 
a  rapid,  coarse  adjustment. 

The  whole  apparatus  can  be  clamped  to  a 
table  at  any  convenient  angle.  It  is  better  to 
use  it  in  a  position  nearly  vertical  and  at  about 
the  level  of  the  eyes  of  a  seated  observer. 

An  additional  precaution  which  it  is  well  to  take  in 
working  with  visual  percepts  is  to  cover  all  parts  of  the 
field  not  directly  involved  in  the  percept.  A  screen  of 
gray  cardboard  with  a  circular  or  elliptical  opening  in  the 
center,  cut  large  enough  to  allow  the  lines  to  be  seen, 
but  not  to  expose  any  of  the  apparatus  near  the  lines,  is 
the  most  convenient  means  of  avoiding  distractions  from 
the  outlying  visual  objects.  Such  a  screen  can  be  tacked 
over  the  apparatus  described  above. 


22 


LABORATORY  EQUIPMENT  FOR 


B — RESULTS 

A  table  showing  the  results  of  a  series  of  measurements 
which  emphasizes  to  an  unusual  degree  the  difference 
between  the  two  types  of  setting,  but  is  otherwise  typical, 
may  be  given  as  follows : 

Table  I 

Observer  J.  C.  B.  Figure,  Miiller-Lyer;  10  cm.,  3  cm.,  45°.    Mch.  10. 
All  measurements  reported  in  millimeters. 


Illusion  when 
B  is  too  long 
at  beginning. 

Variation 
from  avg. 
of  five. 

Illusion  when 
B  is  too  short 
at  beginning. 

Variation 
from  avg. 
of  five. 

Variation 
from  gen. 
average. 

24.0 

0.6 





3.8 

24.0 

0.6 

.... 



3.8 

26.5 

1.9 



6.3 

24.5 

0.1 





4.3 

24.0 

0.6 

.... 

.... 

3.8 

.... 

.... 

16.5 

0.7 

3.7 

.... 

.... 

14.5 

1.3 

5.7 



15.0 

0.8 

5.2 

.... 

16.0 

0.2 

4.2 





17.0 

1.2 

3.2 

Avg.  24.6 

M.V.0.76 

15.8 

M.V.0.84 



General. 

General  average  for  10  determinations  20.2      M.V.  4.4 

A  general  table  showing  the  results  for  various  figures 
examined  by  the  same  observer  is  as  follows: 

Table  II 
Observer  J.  C.  B.     Date,  March  10. 


Figure 

Avg.  10  determinations 

M.V.     ! 

10  cm.,  1  cm.,  45° 

12.6 

1.1 

10     «     2     «     45° 

18.0 

3.1 

10     «     3     «     45° 

20.2 

4.4 

10     «     4     «     45° 

22.7 

3.5 

10     «     5     u     45° 

23.0 

3.7 

PSYCHOLOGICAL  EXPERIMENTS 


23 


A  table  presenting  the  results  for  a  group  of  observers 
using  various  figures  is  as  follows: 

Table  III 


Figure 

10,  1,  45° 

10,  3,  45° 

10,  5,  45° 

10,  3,  30° 

10,  3,60° 

Subject 

Avg. 

M.  V. 

Avg. 

M.  V. 

Avg. 

M.  V. 

Avg. 

M.V. 

Avg. 

M.V. 

A.B.C. 
D.E.F. 
G.H.I. 
J.K.L. 
M.N.O. 

15.1 
11.0 

12.6 

3.4 
2.1 
3.0 

23.3 
15.7 
21.2 
19.0 

4.75 
2.1 
4.2 
3.5 

31.8 
21.1 
27.0 

2.6 
2.7 
3.9 

7.0 
19.1 

3.3 
1.3 

0.0 

15.1 

3.4 
1.8 

26  7 

3  0 

The  results  reported  in  Table  II  are  represented  in  the 
curve  shown  in  Fig.  11.     Similarly  the  results  reported 


SCO). 


FIG.  H 


24          LABORATORY  EQUIPMENT  FOR 

in  Table  III  for  the  first  three  observers  are  given  in  the 
curves  in  Fig.  12. 

C — SUPPLEMENTARY   EXPERIMENTS 

The   first   supplementary   experiment   deals   with    the 
Poggendorff  illusion  (Fig.  13).     The  lines  A  and  B  and 


1 


FIG. 12 

the  space  between  B  and  C  should  be  drawn  on  one  card ; 
the  lines  C  and  D  on  a  second  card.  The  two  cards  can 
now  be  adjusted  on  each  other  in  the  same  way  as  the  cards 
in  the  case  of  the  Miiller-Lyer  figure,  until  A  and  D  seem 
to  extend  in  the  same  direction.  There  is  another  method 
of  treating  this  illusion;  namely,  by  rotating  one  or  both 


PSYCHOLOGICAL  EXPERIMENTS 


25 


of  the  lines  A  and  D  until  they  seem,  because  of  their  ro- 
tation, to  extend  in  the  same  direction.  The  method 
of  measuring  rotations  is  more  complex  than  the  method 
of  sliding  the  cards  back  and  forth  over 
each  other.  The  principle  involved  in  the 
rotation  method  will  be  described  later  in 
a  case  in  which  it  is  clearly  required, 
namely,  in  measuring  the  Zollner  illusion. 
The  second  supplementary  experiment 
deals  with  such  an  illusion  as  that  shown 
in  Fig.  14,  where  the  point  is  in  reality 
equally  distant  from  the  two  circles,  but  seems  to  be 
nearer  to  the  large  circle.  In  attempting  to  draw  the 
two  parts  of  this  figure  on  cards  for  purposes  of  adjust- 
ment in  a  way  analogous  to  that  described  for  the  earlier 
figures,  a  difficulty  which  has  not  been  serious  up  to  this 
point  makes  itself  emphatically  felt.  The  line  of  division 
between  the  two  cards  forms  in  reality  an  additional  object 
in  the  field  of  vision,  and  its  presence  can  not  be  ignored 


FIG.  13 


o 


FIQ. 14 


in  trying  to  locate  a  point  between  two  figures.  The 
method  must,  accordingly,  be  modified  in  such  a  way  as 
to  make  it  possible  to  present  two  circles  in  the  field  of 


26          LABORATORY  EQUIPMENT  FOR 

vision  with  an  intermediate  point  which  shall  in  no  way 
be  associated  with  a  line  of  division  between  cards. 

The  simplest  method  of  meeting  this  demand  is  to  draw 
the  circles  on  a  large  card  and  then  draw  the  point  which 
is  to  be  placed  between  them  on  the  back  of  a  glass  which 
is  large  enough  to  cover  the  whole  field.  The  glass  with 
the  point  on  its  back  surface  may  now  be  shifted  over  the 
fixed  card  until  the  point  is  in  the  desired  position.  The 
glass  with  the  point  may  be  fastened,  if  desired,  to  the  ad- 
justable strip  CC  of  the  apparatus  shown  in  Fig.  9  (p.  18). 
The  glass  may  be  fastened  by  boring  holes  through  it  and 
screwing  it  to  the  board,  or  by  fastening  along  one  edge 


I    I    I    I    I    I    I    I    I  I 

»  vi  4 

FIG.  15 

either  heavy  gummed  paper  or  electric  tape,  and  fastening 
the  paper  or  tape  to  the  board. 

The  method  just  described  can  easily  be  applied  to  the 
measurement  of  the  illusions  of  interrupted  space  shown 
in  Fig.  15.  The  distances  XY  and  X'Y'  of  these  figures 
are  equal  to  YZ  and  Y'Z'.  The  point  Z  and  the  short 
line  Z'  may  be  drawn  on  the  back  of  a  glass,  and  may 
then  be  adjusted  until  XY  seems  equal  to  YZ,  or  X'Y' 
equal  to  Y'Z'. 

Another  method  of  carrying  out  the  experiments  with 
circles  of  unequal  size  or  filled  and  empty  space  consists 
in  taking  the  observer  into  a  dark  room,  and  providing 
conditions  of  illumination  which  shall  make  it  possible 


PSYCHOLOGICAL  EXPERIMENTS          27 

to  manipulate  the  figures,  without  introducing  any  irrele- 
vant object  whatsoever  into  the  field  of  vision.  This  can 
be  readily  done  as  follows:  Provide  a  box,  one  face  of 
which  consists  of  a  milk  glass  which  will  distribute  the 
light  falling  upon  it  as  uniformly  as  possible.  This  milk 
glass  should  be  illuminated  by  a  light  placed  within  the 
box.  A  black  square  or  circle  may  be  produced  upon  this 
surface  by  means  of  an  opaque  figure  which  will  inter- 
cept the  light  supplied  to  the  milk-glass  surface  from 
within  the  box.  In  the  same  way  a  dark  point  at  any  de- 
sired distance  from  the  figure  may  be  produced  by  a  black 
point  on  the  milk  glass.  A  second  figure  of  any  shape 
or  size  desired  can  now  be  introduced  on  the  back  side  of 
the  milk  glass,  and  can  be 
moved  nearer  to  the  fixed 
point,  or  further  from  it,  by 
means  of  a  rod  which  extends 
directly  into  the  box  in  such  a 

way  as  not  to  cast  a  shadow 

i          .11     i  <•  FlQ- 

upon   the  milk-glass    surface. 

The  position  of  the  adjustable  figure  can  be  measured 
either  directly  by  means  of  a  scale  or  by  means  of  some 
recording  device  attached  to  the  movable  rod.  This 
general  method  of  escaping  complicating  objects  in  the 
field  of  vision  by  using  illuminated  surfaces  and  black 
objects  can  also  be  applied  to  other  figures  than  the  one 
in  question. 

One  of  the  illusions  of  direction  resulting  from  lines 
crossing  the  main  line  of  the  figure  is  that  which  appears 
in  the  so-called  Zollner  pattern,  Fig.  16.  The  apparatus 
for  the  measurement  of  this  illusion  is  somewhat  more 
complicated,  because  the  direction  of  the  line  is  to  be 
measured  and  not  its  length.  The  simplest  device  b 
as  follows:  One  of  the  long  lines  of  the  Zollner  pattern 


28          LABORATORY  EQUIPMENT  FOR 

with  its  obliques  is  drawn  upon  a  card,  and  at  a  suitable 
distance  from  the  end  of  the  long  line  and  at  the  same 
horizontal  level  as  the  lower  end  of  the  line,  a  black  silk 
thread  is  fastened  to  the  white  card.  This  thread  should 
be  114.5  cm.  (or  some  fraction)  in  length,  in  order  to  facili- 
tate angular  measurement.  At  a  distance  from  the  point 
of  fastening  which  is  equal  to  the  length  of  the  long  line 
of  the  Zollner  pattern,  the  thread  should  be  made  to  pass 
behind  a  screen,  which  will  thus  cut  off  a  suitable  por- 
tion of  the  thread  to  be  compared  with  the  long  line  of  the 
Zollner  pattern.  The  thread  should  be  kept  under  tension 


Fio.  17 

at  its  remote  end  by  a  weight  or  rubber  band.  Let  the 
position  of  the  thread  be  adjusted  by  the  observer  until  its 
direction  seems  to  him  to  be  exactly  parallel  with  the  long 
line  of  the  Zollner  pattern.  The  deviation  of  the  long 
thread  from  the  position  of  true  parallelism  with  the  line 
of  the  Zollner  pattern  can  then  be  read  on  a  scale.  The 
amount  of  this  deviation  constitutes  a  measure  of  the 
illusion. 

A  piece  of  apparatus,  which  in  a  somewhat  more  elabo- 
rate form  follows  the  principles  already  described,  is  shown 


PSYCHOLOGICAL  EXPERIMENTS          29 

in  Fig.  17.  An  outer  frame  A  A  carries  a  piece  of  plate 
glass  on  the  back  of  which  is  drawn  a  plain  straight  line. 
This  line  can  easily  be  drawn  on  glass  by  means  of  an 
ordinary  ruling  pen  and  very  thick  India  ink.  The  frame 
with  the  glass  can  be  rotated,  by  means  of  the  handle  B, 
about  a  rod  fastened  to  the  frame  at  the  back;  and  when 
the  glass  is  so  rotated  it  carries  with  it  the  long  arm  C. 
Held  rigidly  at  the  same  center  as  that  around  which  the 
glass  and  frame  rotate  is  a  wooden  panel  DD,  to  which  is 
tacked  any  desired  part  of  the  Zollner  figure.  The  fixed 
panel  has  connected  with  it  the  long  arm  E.  The  observer 
is  required  to  rotate  frame  AA  with  the  arm  C  about  the 
fixed  panel  D,  until  the  plain  line  and  the  long  line  of  the 


Zollner  patterns  seem  to  him  to  be  parallel;  the  degree 
of  rotation  is  indicated  much  enlarged  at  the  ends  of  the 
arms  C  and  E.  At  the  extreme  ends  of  these  arms  are 
placed  pin-points,  which  may  be  used  to  mark  a  paper  strip 
and  leave  a  permanent  record  of  the  relative  positions  of 
the  arms.  The  device  for  making  the  pin  impressions  is 
represented  in  Fig.  18,  and  operates  by  means  of  the  strings 
FF,  which  are  carried  to  a  point  within  easy  reach  of  the 
observer  who  is  seated  before  the  frame  and  panel.  The 
arm  E  carries  at  its  end  a  wooden  plate  over  which  is 
drawn  a  strip  of  paper  seen  at  P.  Above  and  below  the 
paper  are  pin-points  which  are  held  back  from  the  paper 
by  coil  springs.  The  pins  are  driven  into  the  paper 


30          PSYCHOLOGICAL  EXPERIMENTS 

whenever  the  strings  at  FF  are  pulled  by  the  observer. 
If  with  this  attachment  the  distance  is  recorded  between 
the  pin-points  attached  to  the  fixed  arm  E  and  the  movable 
arm  C,  and  if,  further,  the  distance  of  the  pin-points  from 
the  center  of  rotation  is  properly  chosen,  as  for  example 
114.5  cm.,  the  apparent  deflection  of  the  line  of  the  Zoll- 
ner  pattern  from  its  true  position  can  easily  be  measured 
at  once  in  centimeters  and  degrees  of  arc. 

For  the  remaining  supplementary  experiments  it  is 
only  necessary  to  make  measurements  with  one  or  the  other 
of  the  methods  above  described,  and  to  tabulate  the  re- 
sults fully  as  indicated  in  the  table  and  curve  given  for 
such  a  practice  series  in  the  general  introduction  (page 
13). 


EXERCISE  II 

A — APPARATUS  AND  PROCEDURE 

In  all  experiments  dealing  with  monocular  vision  it  is 
better  to  cover  one  eye  with  a  loose  shield  rather  than  to 
bind  the  eye  or  require  the  observer  to  keep  the  eye  closed 
by  voluntary  effort.  A  simple  shield  for  the  eye  can  be 
made  of  stiff  cardboard  covered  with  dark  cloth.  The 
shield  should  be  large  enough  to  cover  the  region  from 
the  eyebrows  to  the  cheek  bone,  and  from  the  bridge  of 
the  nose  to  the  temple.  It  should  be  bent  in  its  vertical 
axis  and  shaped  at  the  sides  so  that  the  right  and  left 
edges  will  fit  against  the  face  as  closely  as  possible.  It 
can  be  held  in  position  by  means  of  a  rubber  band  about 
the  head. 

A  second  general  requirement  in  monocular  experi- 
ments is  a  head-rest.  If  table  clamps  and  S-clamps  and 
rods  (page  9)  are  included  in  the  general  equipment 
of  the  laboratory,  a  simple  and  satisfactory  head-rest 
can  be  set  up  without  special  additions  to  the  general 
equipment.  Let  a  horizontal  rod  be  supported  on  a  table 
by  two  upright  rods  at  the  level  of  a  seated  observer's 
upper  teeth.  Since  the  head  naturally  tends  to  drop  for- 
ward, and  since  the  upper  teeth  are  firmly  fixed  in  the  skull, 
it  follows  that  any  support  placed  under  the  upper  teeth 
will  give  the  head  a  firm  rest.  Any  other  point  of  the 
skull  which  might  be  used  for  the  same  purpose  has  the 
disadvantage  of  being  covered  with  loose  skin  which  per- 
mits more  or  less  movement  of  the  head  against  the  rest. 
If  it  is  desirable  that  the  head  be  brought  to  the  same 

31 


32 


LABORATORY  EQUIPMENT  FOR 


M  S 


position  in  a  number  of  successive  experiments,  or  if  it 
is  necessary,  as  in  this  exercise,  to  hold  the  head  in  the  same 
position  for  a  long  time,  the  fixation  of  the  teeth  can  be 
made  much  more  complete  by  covering  the  supporting 
bar  with  a  layer  of  sealing-wax  into  which  the  teeth  may 
be  pressed  while  the  wax  is  warm.  The  mold  of  the 
teeth  thus  produced  upon  the  bar  can  be  used  to  bring 

the  head  back  into  its  original 
position  even  after  the  ob- 
server has  moved  away  for  a 
time.  Instead  of  the  hori- 
zontal rods  just  described, 
a  wooden  strip  small  enough 
to  be  taken  between  the  teeth 
can  be  supported  by  clamps 
from  the  table  or  from  a  chair, 
and  the  upper  teeth  can  rest 
upon  this  wooden  strip. 

It  is  frequently  desirable  to 
have  a  portable  head-rest 
which  can  be  set  up  in  smaller 
space  than  the  table-rest  de- 
scribed. Fig.  19  represents 
a  very  convenient  form  of 
general  head-rest.  A  piece  of 
iron  pipe  P  is  screwed  or 
driven  into  a  heavy  tripod  base  B.  If  it  is  desired,  a 
number  of  pipes  of  different  lengths  may  be  provided  for 
various  purposes.  A  block  of  wood  W,  split  into  halves  and 
having  in  its  center  a  hole  somewhat  smaller  than  the 
iron  pipe,  can  be  clamped  firmly  to  the  pipe  P  by 
means  of  screws  RR,  which  pass  through  the  block  and 
are  provided  with  thumb  nuts  on  one  side.  This 
block  can  be  loosened  by  unscrewing  RR,  and  can  then 


FIG.  19 


PSYCHOLOGICAL  EXPERIMENTS          33 

be  set  at  any  desired  level  up  and  down  on  P.  At 
the  sides  of  the  block  are  fastened  adjustable  strips  of 
iron  as  indicated  in  detail  at  S,  T,  M.  S  is  a  thumb- 
screw which  clamps  the  strip  T  against  the  block.  By 
means  of  the  slot  M  in  the  strip,  the  strip  may  be  made 
to  project  to  any  desired  distance  beyond  the  block. 
This  arrangement  also  makes  it  possible  to  set  the  strip  at 
any  desired  angle,  as  at  B.  At  the  outer  end  of  the  strip 
is  a  device  for  clamping  a  cross  rod.  This  device  con- 
sists in  a  slot  N  in  the  strip  T,  and  a  bent  piece  of  iron 
F,  with  a  double  slot  corresponding  to  the  slot  N  in  the 
long  strip.  The  bent  piece  F  has  a  screw  G  passing 
through  its  middle.  When  now  the  bent  piece  is  slipped 
over  the  strip,  the  three  slots  give  an  opening  which  may 
be  regulated  in  size  by  means  of  the  screw  G.  If  this 
screw  is  set  down  against  the  end  of  the  strip  T,  the  open- 
ing left  between  the  three  slots  can  be  reduced  in  size  so 
as  to  hold  a  rod  firmly  in  position.  A  second  adjustable 
iron  strip  K  is  fastened  on  the  opposite  side  of  the  wooden 
block.  Between  these  two  strips  a  bamboo  rod  can  be 
fastened  in  the  slots  N  N',  and  on  the  rod  a  sealing-wax 
impression  for  the  teeth  can  be  made  as  described  above. 
The  rest  can  be  used  in  two  positions.  Either  the  back  of 
the  head  can  be  placed  against  the  block  and  the  rod 
with  the  teeth-rest  be  adjusted  to  hold  the  head  back 
firmly  against  the  block,  or  the  iron  strips  can  be  set  up 
from  the  wooden  block,  as  in  B,  the  block  acting  in  this 
case  as  a  standard  on  which  to  fasten  the  teeth-rest.  In 
position  T  the  space  in  front  of  the  eyes  is  left  entirely 
free;  in  position  B  the  space  around  the  ears  is  also  left 
free. 

A  perimeter,  which  is  the  most  convenient  device  for 
measuring  positions  on  the  retina  and  stimulating  its 
different  areas,  can  be  constructed  in  very  simple  form 


34          LABORATORY  EQUIPMENT  FOR 

from  a  child's  hoop.  The  hoop  should  be  as  large  as 
possible;  it  should  be  cut  in  two  so  as  to  give  a  half  circle, 
and  it  should  be  graduated  in  degrees.  The  easiest 
method  of  graduating  the  hoop  is  to  determine  by  measure- 
ment the  total  circumference  of  the  hoop  and  then,  after 
dividing  this  by  360,  to  mark  off  by  direct  measurement 
every  -jj-^-  of  the  half  circumference.  The  half  hoop 
should  be  fastened  on  some  kind  of  firm  upright  stand- 
ard, if  necessary  on  the  wall.  Other  points  of  fastening 
may  be  suggested.  Thus,  a  heavy  rod  fastened  to  a  table 
is  a  very  good  holder  and  gives  the  experimenter  better 
opportunity  of  getting  behind  the  perimeter.  Even 
better  is  a  special  base  similar  to  that  described  in  connec- 
tion with  the  head-rest.  The  point  of  fastening  should 
be  on  the  same  horizontal  level  as  the  observer's  eye.  It 
is  often  easier  to  adjust  the  height  of  the  observer  than  of 
the  apparatus.  The  observer  should  be  placed  with  one 
eye  at  the  center  of  the  circle  of  which  the  hoop  forms  the 
circumference;  the  other  eye  should  be  covered;  and  the 
observer  should  be  required  to  look  steadily  at  the  point 
on  the  semicircular  hoop  at  which  it  is  fastened  to  the 
standard.  This  center  should  be  marked  with  a  spot  of 
white  paint  in  order  to  make  it  easy  of  fixation.  The 
position  of  the  perimeter  will  determine  the  part  of  the 
retina  which  is  to  be  examined.  The  most  convenient 
position  is  that  in  which  the  perimeter  is  placed  in  the 
horizontal  plane.  It  may  be  placed  vertically  or  obliquely. 
If  the  whole  retina  is  to  be  examined,  it  must  be  placed 
successively  in  a  number  of  these  positions. 

A  small  disk  of  colored  paper  two  or  three  centimeters 
in  diameter  should  be  attached  to  a  rod  and  should  be 
held  successively  at  various  positions  along  the  graduated 
circumference  of  the  hoop.  It  is  better  that  the  color  be 
exposed  for  a  brief  interval  and  then  withdrawn,  rather 


PSYCHOLOGICAL  EXPERIMENTS          35 

than  exposed  continuously,  as  the  retina  fatigues  very 
easily,  especially  in  its  eccentric  parts.  The  background 
against  which  the  colored  disks  appear  can  be  made 
either  gray  or  black.  It  should,  however,  be  uniform  in 
its  color  tone.  In  certain  elaborate  experiments  with 
the  perimeter,  uniformity  of  background  is  secured  by 
going  into  a  dark  room  and  exposing  the  various  colored 
papers  by  means  of  some  artificial  light  which  can  be 
turned  off  when  the  apparatus  is  not  in  use.  When  the 
observer  is  thus  taken  into  a  dark  room  the  condition  of 
the  retina  is  modified.  It  becomes  dark-adapted  and  its 
sensitivity  to  colors  is  completely  modified.  The  investi- 
gation when  conducted  in  ordinary  daylight  gives  results 
which  are  appropriate  to  an  eye  which  is  light-adapted. 
The  disadvantage  of  trying  an  ordinary  class  experi- 
ment in  a  dark  room  is  that  dark-adaptation  is  not  easy 
either  to  secure  or  maintain.  In  order  that  it  should  be 
complete,  the  observer  must  sit  in  a  dark  room  for  at  least 
fifteen  minutes  and  possibly  more  before  the  beginning  of 
the  experiment.  Furthermore,  every  time  the  light  is 
turned  on  there  is  a  tendency  to  return  to  the  condition 
of  light-adaptation.  The  experiment  must,  therefore, 
proceed  very  deliberately.  If  the  experiment  is  con- 
ducted in  ordinary  daylight,  the  background  should  not 
be  so  bright  as  to  be  dazzling,  and  this  end  is  best  secured 
by  hanging  about  the  perimeter  either  a  gray  paper 
or  gray  cloth.  The  color  then  appears  on  a  uniform 
background. 

A  simple  device  which  is  easy  to  set  up  but  complex 
in  its  measurements,  consists  in  moving  the  eye  rather 
than  moving  the  object  along  the  circumference  of  a  circle. 
In  this  case  the  center  where  colors  are  exposed  consists 
of  a  small  circular  opening  in  a  cardboard  screen.  The 
eye  can  either  fixate  this  opening  directly  or  can  look 


36          LABORATORY  EQUIPMENT  FOR 

at  some  point  at  the  left  or  right  of  this  center.  The  dis- 
tances to  the  right  and  left  of  the  center  of  fixation  being 
measured  directly  as  straight  lines,  a  trigonometric  cal- 
culation is  required  to  reduce  the  measurements  to  de- 
grees. The  simplest  method  of  reduction  is  to  fix  an  eye- 
rest  consisting  of  a  small  ring  at  a  known  distance  from 
the  point  where  the  color  is  exposed,  and  then  after  cal- 
culating the  tangents  for  various  degrees  of  circular  move- 
ment, mark  the  scale  to  the  right  and  left  of  the  opening 
through  which  the  color  is  exposed  in  linear  extents  which 
correspond  directly  to  degrees.  Such  a  graduated  scale 
being  prepared,  the  eye  is  turned  say  to  a  position  80° 
from  the  center  at  which  the  color  is  exposed;  the  color 
may  now  be  exposed  to  the  eye,  and  since  the  eye  has  ro- 
tated outward  through  80°,  the  light  will  fall  on  the  ret- 
ina at  a  point  80°  from  the  center  of  vision.  The  method 
of  exposing  the  colored  paper  in  this  case  consists  in  merely 
uncovering  either  a  piece  of  colored  paper  or  a  source  of 
colored  light.  The  screen  which  has  covered  the  colored 
light  up  to  the  moment  of  exposure  should  be  of  the  same 
intensity  of  gray  as  the  general  background,  which  in  this 
case  consists  of  the  screen  upon  which  the  graduations 
for  the  eye  movement  are  placed.  This  form  of  appa- 
ratus, which  is  known  as  a  campimeter,  has  the  advantage 
over  the  perimeter  that  all  sorts  of  colors  can  easily  be 
placed  under  the  opening  in  the  screen.  Color  mixers 
of  different  forms,  to  which  reference  will  be  made  in 
the  description  of  the  apparatus  for  the  next  exercise,  can 
easily  be  used  in  connection  with  the  campimeter,  while 
they  can  not  be  used  with  any  simple  perimeter. 

Colored  papers  for  this  experiment  and  the  next  can  be 
secured  from  C.  H.  Stocking  Co.,  39  West  Randolph 
Street,  Chicago,  111.,  who  are  the  American  agents  for 
Rothe,  the  mechanic  of  Professor  Hering,  of  Leipzig. 


PSYCHOLOGICAL  EXPERIMENTS          37 

Several  systems  of  papers  have  been  prepared  by  Ameri- 
can manufacturers,  notably  those  prepared  by  Milton- 
Bradley  and  the  Prang  Co.,  but  these  are  inferior  for 
purposes  of  scientific  investigation  to  the  selected  Ger- 
man papers  referred  to  above.  Various  devices  for 
using  transmitted  rather  than  reflected  light  have  been 
prepared.  The  most  successful  of  these  consists  in  col- 
ored gelatines,  which  are  also  of  foreign  manufacture 
and  are  to  be  had  of  Stoelting  Co.  A  number  of  gela- 
tines placed  together  can  be  so  combined  as  to  pro- 
duce colors  that  are  approximately  pure.  They  are, 
however,  by  no  means  as  bright  as  reflected  colors  from 
the  Hering  papers.  Methods  for  the  determination  of 
the  purity  of  colored  fields  and  methods  for  the  deter- 
mination of  the  intensity  of  colored  fields  are  unnecessary 
for  anything  except  the  more  elaborate  tests  of  the  sort 
suggested  in  this  exercise. 

If  it  is  desired  to  make  these  tests,  the  ordinary  spectro- 
scope methods  employed  by  the  physicists  may  be  used 
for  finding  the  quality  of  the  colors.  The  establishment 
of  the  equations  of  like  intensity  of  colors  is  of  somewhat 
greater  importance,  and  a  simple  method  can  be  employed 
as  follows:  Two  colors  which  are  to  be  compared  with 
reference  to  their  intensity  are  brought  into  such  a  position 
that  they  stimulate  the  extreme  periphery  of  the  retina. 
At  this  part  of  the  retina  their  color  qualities  are  entirely 
lost  and  they  are  seen  as  gray.  Their  relative  intensities 
can  now  be  compared  so  as  to  determine  which  is  the 
brighter.  It  is  ordinarily  not  possible  to  change  the 
character  of  the  papers  so  as  to  make  them  equal  in 
intensity,  but  the  results  of  the  equating  of  the  color 
intensities  can  be  recognized  in  evaluating  the  results  of 
experiments  with  the  papers. 

One  of  the  most  common  sources  of  difficulty  in  this 


38          LABORATORY  EQUIPMENT  FOR 

experiment  consists  in  the  inability  of  the  ordinary  ob- 
server to  describe  with  accuracy  his  color  experiences. 
Slight  differences  in  color  qualities  are  not  covered  by  the 
vocabulary  of  many  observers.  As  a  preliminary  to  this 
exercise  it  is  therefore  advantageous  to  spend  some  time 
exhibiting  a  series  of  color  qualities  and  preparing  a  series 
of  designations  for  them.  For  this  purpose  an  excellent 
series  of  color  specimens  and  color  terminology  will  be 

found  in  the  Standard 
Dictionary  under  the 
term  spectrum.  Oth- 
erwise the  observer 
should  be  carefully 
instructed  to  follow 
the  recommendation 
given  in  the  Laboratory 
Manual  of  describing 
each  succeeding  color 
experienced  in  terms 
of  its  differences  from 
the  color  which  im- 
mediately preceded  it. 
Observers  can  very 
frequently  tell  the 
direction  of  a  color 
change  when  they  have  no  adequate  single  phrase  with 
which  to  designate  the  color  itself. 

More  elaborate  forms  of  apparatus  than  those  described 
thus  far  have  been  devised  and  are  available  for  purposes 
of  the  experiment  here  under  discussion.  Perimeters 
are  used  by  oculists  for  the  determination  of  the  retinal 
field  without  reference  to  the  modification  in  the  character 
of  color  vision.  Elaborate  frames  carrying  different  de- 
vices for  holding  and  recording  the  position  of  stimuli 


Fio.  20 
From  the  catalogue  of  Meyrowiti 


PSYCHOLOGICAL  EXPERIMENTS          39 

have  been  prepared.  Several  of  the  more  complete  forms 
of  automatic  recorders  may  be  found  by  consulting  the 
catalogue  of  E.  B.  Meyrowitz,  104  East  23d  Street,  New 
York  City.  (See  Fig.  20,  which  shows  one  of  these.) 

The  metallic  half  circle  here  used  is  supported  on  a  heavy 
base.  At  its  center  the  half  circle  may  be  rotated  through 
every  angle  of  the  complete  sphere.  Its  angular  position 
is  measured  by  a  disk  shown  in  the  figure.  This  disk 
carries  a  printed  chart  of  the  retina,  marked  off  in  degrees. 
An  automatic  recorder  indicates  on  this  chart  the  posi- 
tion of  any  source  of  light  which  moves  along  the  half 
circle.  The  observer,  with  his  head  fixed  in  the  rest 
shown  at  the  right  of  the  figure,  is  seated  in  such  a  posi- 
tion that  the  center  of  his  eye  is  at  the  center  of  the  cir- 
cle of  which  the  half  circle  is  a  part,  and  in  the  same 
horizontal  plane  as  the  center  of  the  perimeter. 

It  is  desirable,  as  noted  above,  that  the  color  which  is 
to  be  exposed  shall  not  be  constantly  visible  to  the  ob- 
server. Various  devices  may  be  suggested,  such  as  cov- 
ering the  color  when  it  is  being  adjusted.  Still  better  is 
the  construction  of  a  perimeter  somewhat  simpler  than  that 
shown  in  Fig.  20,  but  allowing  the  attachment  of  the  light 
box  represented  in  Fig.  21.  A  box  shown  in  outline  at 
AAA  is  painted  black  on  the  outside,  so  that  it  shall  offer 
no  positive  stimulus.  It  is  supplied  inside,  as  shown  at  E, 
with  an  incandescent  lamp.  Some  lamp  which  gives  ap- 
proximately white  light,  such  as  the  tautalum  lamp,  is 
preferable  to  the  ordinary  incandescent  lamp.  The  box 
is  open  at  the  point  F,  there  being  at  this  point  a  small 
circular  opening  2  cm.  in  diameter.  Just  behind  this  open- 
ing and  in  such  a  position  that  it  reflects  the  light  from 
the  lamp  E  is  placed  a  colored  paper  C.  Any  color  may 
be  inserted  at  the  point  C,  and  when  the  box  is  closed  and 
the  lamp  turned  off  the  color  will  be  invisible  to  the  ob- 


40 


LABORATORY  EQUIPMENT  FOR 


server.  By  means  of  a  simple  switch  at  S  the  lamp  E 
may  be  turned  on,  when  the  color  will  immediately  be 
visible.  If  an  ordinary  incandescent  lamp  is  used  at  E 
an  additional  feature  must  be  introduced  into  the  box 
because  the  color  of  the  light  from  such  a  lamp  is  decidedly 
red.  There  must  be  introduced  at  RR  a  layer  of  colored 
gelatine  which  will  modify  the  light  so  as  to  make  the 
light  less  decidedly  red.  A  combination  of  green  and  blue 
gelatine  can  be  secured  which,  held  between  two  sheets 


FIG.  21 

of  glass  in  the  position  RR,  will  modify  the  light  from  E 
before  it  reaches  the  colored  surface  C,  and  give  satis- 
factory color  effects  with  all  papers. 

The  perimeter  and  its  attachments  may  be  of  any  size 
desired.  The  larger  the  circumference,  the  easier  will  be 
the  readings  for  different  positions  of  the  color.  Further- 
more, if  the  base  and  circle  are  made  heavy  enough  they 
may  carry  any  desired  additional  apparatus,  such  as  color 
mixers.  In  the  larger  forms  a  quarter  circle  counter- 


PSYCHOLOGICAL  EXPERIMENTS 


41 


balanced  at  one  end  by  a  heavy  weight  serves  better  than 
a  full  half-circle. 

B — RESULTS 

The  following  table  shows  a  very  good  series  of  observa- 
tions.    In  general  the  observations  are  less  consistent. 

Observer  A.  B.  C.     Right  Eye.     Colors  from  Hering  Papers. 
October  8. 


Red. 

Green. 

Yellow. 

Blue. 

90° 

Nothing 

Light,  without 

Light,  no  color 

Nothing 

color 

80° 

Light,  no  color 

Light,  without 

Light,  no  color 

Possibly 

color 

red 

70° 

Possibly  red 

Orange,  pale 

Yellow,  distinct 

Pale  yellow 

60° 

Yellow,  dis- 

Yellow, pale 

Yellow,  no 

Blue,     dis- 

tinct 

change 

tinct 

50° 

Yellow,  toward 

Orange 

Yellow,  no 

Blue,  paler 

orange 

change 

40° 

Orange 

Yellow,  pale 

Yellow, 

Blue, 

brighter 

brighter 

30° 

Red,  distinct 

Very  pale,  pos- 

Yellow, same 

Blue,  very 

sibly  green 

as  last 

clear 

20° 

Red,  distinct 

Green 

Yellow,  same 

Blue, 

brighter 

10° 

Red, 

Green, 

Yellow, 

Blue,  same 

brighter 

brighter 

brighter 

0° 

Red 

Green 

Yellow 

Blue,  same 

Fig.  22  shows  graphically  the  results  of  a  series  of  such 
observations  for  a  class.  The  letters  represent  the  vari- 
ous observers.  The  general  result  is  here  made  obvious 
and  agrees  with  the  special  table  reported  above.  It  will 
be  seen  from  the  figure  that  not  all  observers  show  so 
marked  a  difference  as  is  shown  in  the  table  between  red 
and  green  on  one  hand,  and  yellow  and  blue  on  the  other. 


42          LABORATORY  EQUIPMENT  FOR 

C — SUPPLEMENTARY   EXPERIMENTS 

Among  the  additional  problems  described  under  Exer- 
cise II,  is  one  for  plotting  the  projection  of  the  blind-spot. 
No  elaborate  apparatus  is  necessary  for  this  experiment. 
Any  means  of  holding  the  head  in  a  fixed  position  before 
a  large  white  surface  will  satisfy  the  requirements.  A 
block  of  wood  25  cm.  in  length,  placed  upon  a  table,  fur- 
nishes the  simplest  head-rest.  If  the  teeth  rest  against 
the  upper  end  of  the  block,  and  the  eye  is  allowed  to  fixate 

0o  ;0o        20°        30°        40°       60°        60°        70°        80*        90° 

fiea       .—-—_««____ 
8.  M.        J.  H.    f.  Q.  T.  Qr.  To.    Me. 


Green 


F.  T.  Me.        J.  S.        H.        C.  Q.  M.        Qt.        Ta. 


C.  T.    H.J.S.Ta.  O.F.Mc.    M.Q. 


Blue 


Me.  •        T.8.        C.Ta.6.  Qr.F.J.      H.M. 

Fio.  22 


a  point  on  a  sheet  of  paper  lying  flat  on  the  table  under 
the  block,  the  eye  can  be  held  nearly  enough  in  one  posi- 
tion to  permit  the  experiment  to  go  forward.  If  the  right 
eye  is  used,  the  point  of  fixation  should  be  somewhat  left 
of  the  center  of  the  paper,  and  conversely,  if  the  left  eye  is 
to  be  used,  the  point  of  fixation  should  be  on  the  right. 
After  the  head  has  been  brought  into  position  and  the  eye 
fixed  upon  the  point  drawn  on  the  paper,  a  strip  of  paper 
with  a  black  spot  at  the  end  should  be  brought  into  the 


PSYCHOLOGICAL  EXPERIMENTS          43 

field  of  vision  and  should  be  moved  about  until  the  spot 
can  not  be  seen.  Evidently  the  spot  is  now  within  the 
area  which  casts  its  image  on  the  blind-spot.  In  order  to 
determine  the  boundary  of  this  area  the  spot  should  be 
slowly  moved  to  the  right  or  left  until  it  can  just  be  seen 
by  the  observer.  At  the  point  where  it  becomes  visible 
after  being  in  the  blind-spot,  it  is  evidently  emerging  from 
the  projection  of  the  blind-spot  and  the  fact  should  be 
recorded  on  the  paper  by  means  of  a  point.  The  movable 
strip  of  paper  is  now  drawn  back  so  that  the  spot  falls 
in  the  blind  area  again;  it  is  again  moved  gradually  for- 
ward until  it  appears  at  some  other  point  on  the  boundary 
of  the  blind  area  where  a  second  point  is  marked.  In 
this  fashion  a  sufficient  number  of  points  may  be  definitely 
described  on  the  edges  of  the  area  to  indicate  the  outline 
of  the  projection  of  the  blind-spot.  Two  cautions  are 
necessary.  It  is  better  to  determine  the  boundaries  of  the 
projection  by  drawing  the  point  out  of  the  area  than  by 
moving  it  into  the  blind  area  from  some  part  of  the  field 
where  it  is  visible.  If  the  point  is  moved  into  the  area 
from  the  parts  of  the  field  where  it  is  visible,  its  movement 
can  be  seen  and  there  is  a  strong  natural  tendency  to  fol- 
low its  movement.  Secondly,  the  eye  must  be  steadily 
fixed  on  the  point  marked  on  the  paper,  otherwise  the  out- 
line of  the  blind  area  will  not  be  determined  with  exactness, 
for  with  every  movement  of  the  eye  the  position  of  the  blind- 
spot  changes. 

If  a  convenient  head-rest  is  at  hand,  such,  for  example, 
as  that  described  on  page  32,  it  should  be  used  instead 
of  the  block  above  described,  and  the  observer  should  be 
allowed  to  look  at  a  large  sheet  of  paper  which  has  been 
hung  vertically  in  front  of  the  face.  The  further  procedure 
is  exactly  the  same  as  in  the  first  case. 

The  second  supplementary  experiment  under  this  ex- 


44          LABORATORY  EQUIPMENT  FOR 

ercise  requires  that  the  degree  of  apparent  curvature  of  a 
straight  line  at  the  periphery  of  the  field  of  vision  be 
measured.  As  in  the  earlier  parts  of  the  experiment,  let 
the  head  be  held  in  a  fixed  position  and  the  eye  fixated 
upon  a  determined  point.  Arrange  on  the  edge  of  the  field 
of  vision  a  series  of  points  in  such  a  relation  that  they 
will  seem  to  the  observer  to  extend  in  a  straight  vertical 
line.  They  will,  in  reality,  describe  an  arc  rather  than  a 
straight  line,  and  the  degree  of  the  curvature  can  be  readily 
determined. 

The  third  supplementary  exercise  suggested  on  page 
25  of  the  Laboratory  Manual  can  readily  be  set  up  by 
drawing  on  white  cards  black  geometrical  figures.  The 
figures  should  have  a  general  diameter  of  about  3  cm.,  and 
should  be  exposed  on  a  perimeter  or  with  the  aid  of  a 
campimeter,  as  indicated  in  the  experiments  with  colors. 
If  the  results  for  these  figures  are  tabulated  and  compared 
with  the  results  for  the  various  colors,  it  will  be,  found  that 
there  are  no  intermediate  zones  of  partial  sensitivity  for 
these  figures.  It  will  also  be  found  that  only  the  central 
parts  of  the  retina  which  are  highly  enough  developed  to 
give  complete  color  differentiation  are  highly  enough  de- 
veloped to  make  possible  the  recognition  of  forms. 

To  determine  the  sensitivity  of  different  parts  of  the 
retina  for  slight  changes  in  illumination,  prepare  series  of 
cards  with  gray  circles  of  different  intensities  on  a  black 
background.  Graded  grays  for  this  purpose  can  be  ob- 
tained from  Stocking  Co.  The  first  card  of  this  series 
should  show  very  little  contrast,  the  second  more,  the 
third  still  more,  and  so  on.  By  successive  trials  one  card 
can  be  found  for  each  part  of  the  retina  which  gives  the 
just  recognizable  contrast.  The  procedure  here  is  similar 
to  that  followed  in  exposing  colors  to  the  different  parts 
of  the  retina.  Beginning  with  a  very  slight  contrast,  ex- 


PSYCHOLOGICAL  EXPERIMENTS          45 

pose  it  to  various  parts  of  the  retina  and  determine  where, 
if  at  all,  it  can  be  recognized.  After  this  increase  the 
contrast  and  again  expose  to  different  parts  of  the  retina. 

Another  method  of  determining  the  sensitivity  of  differ- 
ent parts  of  the  retina  is  to  measure  the  amount  of  change 
in  the  intensity  of  light  which  is  necessary  to  arouse  in 
the  observer  the  recognition  of  the  fact  that  the  intensity 
is  changing.  The  observer  may  be  allowed  first  to  look 
at  an  area  that  is  illuminated  from  behind  by  means  of  a 
certain  source  of  light.  If  now  the  source  of  light  is 
moved  steadily  away,  the  intensity  of  its  illumination  will 
be  decreased  in  the  well-known  physical  ratio  according 
to  which  the  intensity  of  a  given  light  is  inversely  propor- 
tional to  the  square  of  its  distance.  If,  therefore,  we 
measure  the  distance  through  which  such  a  light  must  be 
moved  in  order  to  give  a  just  noticeable  increase  or  de- 
crease in  the  illumination,  we  have  a  measure  for  the  sen- 
sitivity of  that  part  of  the  retina.  Care  must  be  taken  in 
such  an  experiment  as  this  to  move  the  light  at  a  uniform 
rate.  The  experiment  can  be  carried  out  most  easily  in 
a  dark  room.  It  is  also  advantageous  where  possible  to  in- 
troduce into  the  field  of  vision  two  illuminated  areas,  one 
of  which  is  kept  at  the  original  intensity  and  the  second 
one  of  which  is  modified  in  the  manner  just  described. 
Such  determinations  may  be  carried  out  for  different  parts 
of  the  retina.  The  method  here  suggested  is  the  regular 
method  of  photometry  and  will  be  described  again  in 
another  connection.  (See  page  131.) 

Experiments  of  this  type  give  different  results  when  the 
eye  is  dark-adapted  than  when  it  is  light-adapted. 

If  the  experiment  is  to  be  made  for  the  dark-adapted 
eye  and  a  dark  room  is  not  available,  a  substitute  for  the 
dark  room  can  be  provided  by  constructing  a  large  box 
which  can  be  made  so  as  to  exclude  light  except  at  the  points 


46          PSYCHOLOGICAL  EXPERIMENTS 

where  it  is  admitted  for  experimental  purposes.  Such  a 
box  should  be  painted  black  inside  and  should  be  pro- 
vided at  one  end  with  a  hood  which  can  be  thrown  over 
the  observer's  head  so  as  to  exclude  all  light  from  that  end. 
At  the  end  of  the  box  opposite  the  observer  a  screen  may 
be  provided  which  is  perforated  with  any  desired  number 
of  openings.  The  intensity  of  illumination  which  is  al- 
lowed to  come  through  these  openings  can  easily  be  regu- 
lated. One  convenient  method  of  reducing  the  light  is 
to  hold  in  front  of  the  opening  a  number  of  sheets  of  thin 
paper.  The  number  of  sheets  of  paper  necessary  to  pro- 
duce a  just  perceptible  difference  in  the  illumination  of 
two  neighboring  points  furnishes  a  rough  but  convenient 
method  of  measuring  that  difference.  A  more  exact 
method  is  to  interpose  a  series  of  plates  of  milk  glass  be- 
tween the  source  of  light  and  the  observer,  and  to  control 
the  area  of  each  of  these  glasses  through  which  light  may 
pass  by  means  of  an  adjustable  diaphragm  such  as  that 
shown  in  Fig.  33,  page  67.  The  successive  plates  of 
glass  and  their  diaphragms  may  be  enclosed  in  a  box  so 
as  to  secure  light  from  one  source  only. 

In  all  of  these  experiments  it  is  highly  important  that 
fatigue  and  after-images  should  be  avoided.  These  can 
be  avoided  by  allowing  sufficient  intervals  to  elapse  be- 
tween successive  experiments. 

The  last  supplementary  experiment  deals  with  the 
matter  of  adaptation  to  light  and  darkness  and  requires 
no  new  methods. 


EXERCISE  III 

A — APPARATUS   AND    PROCEDURE 

The  best  introduction  to  this  exercise  consists  in  showing 
the  observer  a  solar  spectrum  in  which  the  different 
colors  are  exhibited  in  their  natural  intensity  and  order. 
Such  a  solar  spectrum  can  be  produced  by  allowing  a 
pencil  of  sunlight  to  fall  upon  an  ordinary  prism.  The 
rays  coming  from  a  prism  may  be  projected  upon  a  screen 
or  may  be  examined  directly  by  the  observer.  Still  better, 
let  the  observer  look  into  a  spectroscope,  which  has  the 
advantage  over  the  prism  of  magnifying  very  much  the 
color  areas  and  of  rendering  the  different  qualities  much 
more  distinct. 

For  purposes  of  experiments  with  color,  the  light  from  a 
solar  spectrum  is  very  difficult  indeed  to  control,  and,  ex- 
cept with  the  most  elaborate  equipment,  it  can  not  be  used. 
For  this  reason  recourse  is  commonly  had  to  rays  of  light 
reflected  from  colored  paper  surfaces.  The  light  which 
comes  from  colored  surfaces  can  be  controlled  within  wide 
limits,  both  in  quantity  and  in  position,  and  can  easily  be 
mixed.  No  special  materials  or  methods  beyond  those 
described  in  connection  with  the  last  exercise  are  necessary 
to  make  possible  the  first  part  of  the  experiment. 

The  first  and  simplest  method  of  mixture  is  to  utilize 
such  a  reflection  apparatus  as  is  represented  in  Fig.  23. 
This  apparatus  consists  of  two  boards  placed  at  right 
angles  to  each  other.  Between  these  two  boards  is  set  a 
plate  of  plain  glass  which  rests  in  the  angle  between  the 
boards  without  fastening  at  the  bottom.  The  glass  can  be 

47 


48          LABORATORY  EQUIPMENT  FOR 

supported  by  a  string  passing  over  the  top  of  the  vertical 
board  and  can  be  set  at  any  desired  angle  by  adjusting 
the  length  of  the  string.  The  glass  should  be  of  good 
quality  so  that  it  will  have  a  uniform  surface  and  will  be 
as  nearly  transparent  as  possible.  The  observer  should 
look  down  upon  this  plate  of  glass  from  above,  as  indi- 
cated by  the  diagrammatic  eye,  0,  in  the  figure.  If  a 
sheet  of  colored  paper  is  placed  on  the  lower  board  on  the 


Fio.  23 

line  OA,  rays  of  light  from  this  colored  surface  will  pass 
upward  directly  through  the  plate  of  glass  into  the  ob- 
server's eye.  A  second  colored  surface  placed  on  the 
vertical  board  in  the  line  OB  will  send  its  rays  to  the  plate 
of  glass  in  a  horizontal  direction,  and  a  part  of  these  rays 
will  be  reflected  from  the  upper  surface  of  the  glass  and 
will  enter  the  eye  of  the  observer  along  a  path  which  co- 
incides with  that  followed  by  the  rays  from  the  colored 


PSYCHOLOGICAL  EXPERIMENTS 


49 


surface  on  the  horizontal  board.     The  intensity  of  the 
light  along  the  line  B  can  be  modified  by  changing  the 
angle  of  the  glass.     By  this  means   any  desired  colors 
can  easily  be  mixed.     The  limitation 
of  this  method  is  that  it  does  not  per- 
mit of  easy  quantitative  determinations. 
Furthermore,   it    does    not    permit    a 
mixture  of  more  than  two  colors  at  a 
time. 

A  more  common  method  of  mixing 
colors  consists  of  some  system  by  which 
disks  of  colored  paper  can  be  locked  together  and  rapidly 
rotated.  The  simplest  device  of  this  sort  is  a  color-top 
(Fig.  24).  A  simple  wooden  shaft  and  tightly  fitting  ring 
hold  in  position  small  disks  of  colored  paper.  The  whole 
is  rapidly  rotated  by  the  fingers  or  by  some  string  device, 
with  the  result  that  the  colors,  which  are  fastened  to  the 
top,  pass  so  rapidly  in  succession  before  the  eye  that  the 


FIG.  24 


FIG.  25 


effect  produced  by  the  different  colored  surfaces  is  prac- 
tically continuous.  The  disks  used  with  the  top  and  other 
rotating  devices  have  small  circular  openings  in  the  center 


50          LABORATORY  EQUIPMENT  FOR 

and  are  cut  along  one  radius.  Fig.  25,  A,  represents  two 
such  disks  being  slipped  over  each  other  so  as  to  leave  a 
part  of  each  disk  exposed.  The  final  relation  of  the  disks 
is  represented  in  Fig.  25,  B.  Obviously  the  relation  can 
be  varied  at  will  so  as  to  expose  as  much  as  is  desired  of 
either  disk.  In  like  manner,  several  disks  may  be  placed 
together.  Furthermore,  it  will  be  easy  to  measure  the 
amount  of  each  colored  surface  exposed.  For  this  pur- 
pose a  protractor  is  placed  over  the  disks  and  the  area 
of  each  sector  is  recorded  in  degrees.  A  transparent 
celluloid  protractor  is  a  very  convenient  form  for  this 
purpose. 

Colored  papers  suitable  for  this  experiment  have  already 
been  discussed  on  pages  36  and  37.  If  the  papers  are  pur- 
chased for  use  in  laboratories  of  moderate  equipment,  it 
will  generally  be  found  advantageous  to  purchase  the  pre- 
pared disks.  If  the  papers  are  to  be  extensively  used  in  a 
great  variety  of  experiments,  it  is  desirable  to  provide  a 
cutter  which  will  make  it  possible  to  prepare  disks  from 
large  sheets  of  paper.  A  convenient  cutter  may  be  briefly 
described  as  follows:  A  metallic  bar  has  at  one  end  a 
handle  and  a  sharp  point.  The  point  is  driven  through 
the  paper  into  a  board  underneath;  it  now  serves  as  a  cen- 
ter of  rotation  for  the  cutter.  On  the  bar  is  fastened  a 
knife  which  can  be  adjusted  by  sliding  it  along  the  bar 
to  any  desired  distance  from  the  center  of  rotation.  This 
knife  is  pressed  against  the  paper  and  the  disk  cut  out 
by  rotating  the  knife  so  as  to  describe  the  circumference 
of  a  circle. 

The  color-tops  described  offer  such  small  surfaces  to 
the  view  of  the  observer  that  contrast  and  other  distract- 
ing effects  impair  seriously  the  value  of  the  measurements. 
A  mixing  device  which  utilizes  colored  disks  of  larger  size 
made  of  cardboard,  is  included  in  Milton-Bradley's  Pseu- 


PSYCHOLOGICAL  EXPERIMENTS 


51 


doptics.*  This  mixer  takes  advantage  of  a  principle 
which  is  employed  in  a  simple  child 's  toy.  Two  holes 
pass  through  a  small  metal  disk  on  opposite  sides  of  the 
center  of  the  disk.  Through  these  two  holes  are  drawn 
two  strings.  If  now  the  extremities  of  these  strings  are 
held  firmly  in  the  fingers  and  the  string  is  twisted  about 
itself,  the  disk  can  be  set  in  rapid  motion  by  pulling  at 
the  ends  of  the  string.  Such  momentum  can  be  attained 
by  the  disk  in  its  rotation  that  it  will  twist  the  string 
around  itself  in  the  opposite  direction  to  that  in  which  it 
was  twisted  at  first,  provided  the  operator 
relaxes  the  tension  on  the  string  after  the  mo- 
mentum is  well  established.  After  the  disk 
has  wound  the  string  around  itself  it  will 
come  to  rest.  It  can  now  be  set  in  motion  in 
the  opposite  direction  by  again  pulling  on 
the  ends  of  the  string.  The  disk  can  be 
kept  in  successive  rotation  in  one  direction 
and  the  other  by  simply  drawing  and  relax- 
ing the  ends  of  the  string.  The  central  per- 
forated metallic  disk  through  which  the 
string  passes  is  made  in  two  parts  in  the 
color  mixer,  the  two  parts  being  screwed  to- 
gether. Between  these  two  parts  are  clamped 
the  colored  disks  to  be  used  in  the  mixing. 
Pasteboard  disks  must  be  used  in  this  case  rather  than 
paper,  otherwise  the  successive  rotation  in  opposite  direc- 
tions would  result  in  air  currents  getting  between  the 
disks  and  tearing  them.  The  mixer  is  shown  in  section  in 
Fig.  26. 

*The  Milton-Bradley  Co.,  Springfield,  Mass.,  issue  a  collection  of  charts  and 
simple  experimental  devices  for  the  illustration  of  a  number  of  visual  phenom- 
ena. It  was  announced,  after  this  collection  of  charts  and  experiments  had  been 
in  use  some  time,  that  it  was  devised  by  Prof.  Munsterberg.  The  collection  is 
extremely  valuable  as  a  means  of  demonstration  and  laboratory  experiment. 
It  should  be  in  the  hands  of  every  teacher  of  psychology.  The  price  of  the 
three  boxes  is  five  dollars. 


FIG.  26 


52          LABORATORY  EQUIPMENT  FOR 

A  third  form  of  color  mixer  which  utilizes  colored  disks 
consists  of  a  combination  of  wheels  driven  by  the  hand. 
In  order  to  secure  the  proper  speed  for  mixing  colors 

with  such  apparatus,  it  is 
necessary  to  have  a  series 
of  cogs  or  belts  between 
the  handle  and  the  rotat- 
ing shaft  on  which  the 
disks  are  held.  A  satis- 
factory mixer  of  this  type 
is  little,  if  any,  less  ex- 
Fia-  s7  pensive  than  an  electric 

From  the  catalopje^Rothe,  Leipzig.       motor  t(>  ^  described   in 

the  next  paragraph.  It 

should  not  be  purchased  unless  it  is  quite  impossible  to 
secure  proper  electric  connections  for  the  motor.  A  good 
form  of  hand  mixer  made  by  Rothe  in  Leipzig  is  shown 
in  Fig.  27.  Most  of  the  other  hand  mixers  are  unsatis- 
factory. 

A  fourth  device  which  is  very  satisfactory,  consists  in 
rotating  the  colored  disks  by  means  of  an  electric  motor. 
An  ordinary  fan  motor  gives  the  rate  necessary.  The  shaft 
of  such  a  motor  is  supplied  with  an  attachment,  between 
the  two  parts  of  which  the  disks  can  be  clamped.  This 
addition  to  the  shaft  of  the  motor  is  known  as  an  arbor 
and  is  the  same  in  principle  as  the  disk  holder  shown  in 
Fig.  26.  Care  must  be  taken  to  place  the  disks  in  such  a 
relation  that  when  the  motor  rotates  the  air  currents 
will  not  spread  the  disks  apart.  If  paper  disks  are  used, 
an  uncut  disk  of  cardboard  should  be  placed  behind  the 
colored  disks  as  a  backing  disk. 

Some  fan  motors  when  once  set  in  motion  are  likely  to 
continue  rotating  because  of  inertia  for  an  inconveniently 
long  period  of  time.  It  is,  therefore,  desirable  to  pro- 


PSYCHOLOGICAL  EXPERIMENTS          53 

vide  some  sort  of  brake  for  these  motors.  The  most  con- 
venient brake  consists  in  an  electrical  adjustment  by  means 
of  which  the  current,  which  has  been  passing  through  the 
coils  of  the  field  magnet  and  the  armature,  may  be  made 
to  pass  through  the  coils  of  the  field  magnet  only.  By 
such  a  device  the  field  magnet  will  act  as  a  magnet  and 
will  attract  the  armature  so  as  to  bring  it  to  a  standstill. 
The  connections  required  are  represented  in  Fig.  28. 
When  the  key  at  K  is  open,  the  current  passes  through 
the  series  of  connections  1,A,Z,F,3,  Ff ',  4,  that  is,  through 
the  field  and  armature  both.  When  K  is  closed,  the  cur- 
rent passes  through  the  circuit  XI,  X2,  K,  X3,  F,  3, 
Ff,  4,  that  is,  through  the  field  magnets  only. 

The  method  of  procedure  with  the  motor  color  mixer  is 
to  clamp  in  the  arbor  two  sets  of  disks,  one  of  large  size, 
one  of  small  size.  The  larger  outer  set  may  be,  for  ex- 
ample, in  the  first  equation,  red  and  yellow,  the  inner  set 
should  then  be  orange,  white,  and  black.  Or  the  reverse 
relation  may  be  chosen  by  using  small  red  and  yellow 
disks  and  large  disks  of 
orange,  white,  and  black. 
An  arbitrary  combination  of 
such  disks  should  be  rotated, 
and  then  in  successive  trials 
the  correct  relation  should  be 
worked  out  by  readjusting 
the  disks  until  the  same  color 
appears  in  the  inner  and 
outer  areas. 

There  are  certain  devices 
by  means  of  which  the  re- 
lation between  disks  can  be  changed  while  the^  are  in  rota- 
tion. These  do  not  permit  of  fusion  of  two  concentric 
sets  of  disks,  the  matching  must  accordingly  be  between 


54 


LABORATORY  EQUIPMENT  FOR 


two  color  surfaces  placed  side  by  side.  The  great  ad- 
vantage of  changing  the  disks  during  rotation  is  that 
the  effect  of  each  change  is  immediately  seen  without 
stopping  for  the  slow  readjustment  and  trial  necessary  in 
ordinary  mixers.  The  difficulty  in  constructing  such  a 
piece  of  apparatus  as  this  is  that  there  must  be  provision 
for  the  rotation  of  the  disks,  and  at  the  same  time  there 
must  be  some  fixed  portion  of  the  apparatus  which  can  be 
easily  moved  by  the  experimenter  so  as  to  change  the 
amount  of  exposure  of  the  disks.  A  device  constructed 
by  Marbe  which  has  these  parts  is  shown  in  Fig.  29.  It 


Fio.  29 
From  the  catalogue  of  Zimmerman n,  of  Leipzig,  Germany 


consists,  first,  of  a  screw  which  can  adjust  the  length  of  a 
long  catgut  violin  string.  The  string  is  fastened  to  this 
screw  by  means  of  a  swivel  joint  which  makes  it  easily 
possible  for  the  catgut  to  rotate,  while  at  the  same  time  it 
can  be  drawn  backward  and  forward  by  turning  the  screw. 
The  catgut  passes  forward  from  this  screw  to  the  center 
of  a  hard  rubber  disk.  Here  it  passes  over  a  pulley  and 
turns  in  a  direction  perpendicular  to  its  first  direction  and 
passes  outward  to  the  rim  of  the  disk.  It  is  now  turned 
on  a  second  pulley  and  passes  from  this  point  over  a  num- 
ber of  pulleys  describing  a  circle  around  the  back  of  the 
disk.  By  passing  over  these  pulleys,  it  describes  a  circle 


PSYCHOLOGICAL  EXPERIMENTS          55 

which  has  its  center  at  the  point  of  its  first  contact  with  the 
disk.  After  passing  around  the  full  circumference  of  this 
circle,  the  catgut  is  attached  to  a  hard  rubber  ring  which 
is  held  in  position  against  the  tension  of  the  catgut  by  a 
spring.  The  hard  rubber  ring  is  capable  of  moving 
around  the  disk  under  the  tension  of  the  catgut  in  a  clock- 
wise direction,  while  by  virtue  of  the  spring  it  tends  to 
return  to  its  original  position  by  moving  counter-clock- 
wise. This  hard  rubber  ring  has  fastened  on  the  surface 
opposite  to  that  on  which  it  is  connected  with  the  catgut, 
a  colored  disk,  such  as  has  been  described  in  connection 
with  the  color-mixing  motor.  A  second  color  disk  is 
fastened  firmly  in  position  against  the  hard  rubber  disk 
around  which  the  hard  rubber  ring  is  capable  of  rotating. 
The  two  color  disks  are  interlocked  along  radii  in  the 
manner  illustrated  in  Fig.  25.  We  have  thus  provided 
two  colored  disks,  one  of  which  is  capable  of  being  changed 
in  its  position  by  means  of  the  catgut,  the  other  of  which 
is  independent  of  the  catgut.  If  now  the  screw  which  con- 
trols the  length  of  the  catgut  is  turned  back,  the  catgut 
will  draw  the  adjustable  ring  in  a  clockwise  direction  and 
will  change  the  relation  of  the  two  colored  disks  to  each 
other.  If  the  screw  releases  the  catgut  somewhat,  the 
adjustable  ring  will  be  moved  by  its  spring  in  a  counter- 
clockwise direction  and  will  reverse  the  relation  between 
the  two  colored  disks.  The  disk  and  ring  to  which  the 
colored  papers  are  attached  are  mounted  in  bearings 
and  are  made  to  rotate  by  means  of  a  belt  connected  with 
an  electric  motor.  The  movement  of  this  disk  and  ring 
with  the  colored  papers  involves  a  rotation  of  the  catgut 
also,  but  this  was  provided  for  in  the  swivel  joint  described 
above.  This  complex  apparatus  is  hardly  necessary  for 
ordinary  laboratory  work. 


56          LABORATORY  EQUIPMENT  FOR 

B — RESULTS 

The  following  table  presents  in  number  of  degrees  the 
results  of  the  mixtures  required  in  the  exercise: 

169°  Red        +  191°  Green       =111°  Yellow  +210°  Black  +    39°  White 

153°  Red        +  207°  Gr.  Blue  =  228°  Black     +  132°  White 

205°  Red        +  155°  Blue         =  358°  Purple  +      1°  Black  +       1°  White 

96°  Red        +  162°  Green        -I-  102°  Blue      =  253°  Black  +  107°  White 
138°  Yellow  +  168°  Blue         +    64°  Green    =  247°  Black  -I-  113°  White 

71°  Orange  +  127°  Blue         +  162°  Green    =  248°  Black  +  112°  White 

These  equations  are  valid,  of  course,  only  for  the  par- 
ticular colored  papers  used  and  for  the  general  illumina- 
tion under  which  the  conclusions  were  worked  out.  The 
papers  used  in  this  case  were  the  older  Hering  tissue 
papers,  and  the  illumination  was  that  of  a  large  general 
laboratory  in  which  the  light  was  admitted  from  large 
windows  about  three  sides  of  the  room. 

A  convenient  graphic  device  for  representing  the  re- 
sults of  mixtures  from  a  group  of  observers  is  represented 
in  Fig.  30.  The  areas  at  the  left  represent,  in  each  case, 
the  relative  amounts  of  colors  necessary  to  match  com- 
binations of  gray  with  the  intermediate  colors  repre- 
sented on  the  right.  The  areas  given  were  secured  by 
averaging  the  results  obtained  from  a  class  of  fifteen 
students.  By  comparing  the  various  figures  for  the  succes- 
sive combinations  with  each  other,  it  will  be  seen  that 
the  general  law  of  color  mixing  is  clearly  brought  out. 

It  will  sometimes  occur  in  a  laboratory  class  that  some 
member  will  exhibit  a  form  of  color-blindness  which  will 
appear  from  the  abnormal  character  of  his  equations. 
Tests  for  such  color-blindness  have  been  carefully  pre- 
pared, and  it  is  better  to  use  one  of  the  regular  tests  than 
merely  to  try  rough  experiments.  A  rough  test  may, 
indeed,  be  made  by  collecting  a  series  of  commercial 
wools  of  different  dyes.  These  being  placed  together  in 


PSYCHOLOGICAL  EXPERIMENTS 


57 


an  unassorted  mass,  the  observer  is  requested  to  take  out 
those  which  seem  to  him  to  match  even  remotely  some 
vivid  green  or  red.  If  he  successfully  passes  the  test  for 
red  and  green  it  is  probable  that  he  is  not  color-blind. 
The  use  of  names  for  the  color-blind  test  is  very  mislead- 
ing, for  many  persons  who  have  a  clear  recognition  of  the 
different  simple  colors  are  unable  to  give  the  names  of 
these  colors,  while,  on  the  other  hand,  persons  who  have 


Equal 


.Red 

Yellow 

G 

R 

A 

Orange 

Y 

Red 

Green 

Equal 


Gray 

Yellow 

Red 

Blue-green 

Equal 


Gray 


Red 

Blue 

G 

R 
A 

Purple 

Y 

Equal 


FIG.  30 

some  defect  in  color  vision  have  learned  enough  of  the 
relation  between  various  color  names  and  the  experiences 
which  they  have  derived  from  the  different  colored  lights 
to  stand  a  test  even  better  than  some  normal  individuals. 
The  special  tests  are  worked  out  by  putting  together  a 
number  of  confusion  colors  which  to  the  normal  eye  are 
clearly  distinguishable,  but  to  the  abnormal  eye  seem 
alike.  One  of  the  best  of  these  tests  is  that  prepared  by 


58          LABORATORY  EQUIPMENT  FOR 

the  physiologist,  Nagel,  who  is  himself  color-blind.  The 
cards  may  be  had  by  addressing  Professor  Nagel,  Uni- 
versity of  Berlin,  Berlin,  Germany,  or  will  be  supplied  by 
the  Yale  Psychological  Laboratory. 


C — SUPPLEMENTARY   EXPERIMENTS 

The  first  supplementary  experiment  deals  with  the 
facts  generally  classified  as  light  contrast  and  color  contrast. 
To  get  a  good  illustration  choose  some  complex  color,  such 
as  a  dark  reddish  brown.  Place  a  small  piece  of  paper  thus 
colored  on  a  bright  red  background  and  another  piece 
with  exactly  the  same  color  on  a  dark  green  background. 
On  the  red  ground  it  will  seem  very  dark  and  dull  in  color. 
On  the  green  it  will  seem  lighter  and  decidedly  more  red 
in  quality. 

In  general  the  experiments  in  light  and  color  contrast 
are  most  effective  when  the  background  is  large  and  the 
contrasting  color  small.  Furthermore,  the  contrast  is 
most  effective  when  the  general  intensity  of  illumination 
of  the  fields  is  not  great.  The  desired  reduction  of  illu- 
mination can  be  secured  by  covering  the  contrasted  papers 
with  thin  tissue  paper.  Contrast  effects  appear,  finally, 
most  clearly  when  shades  of  little  saturation  are  placed 
upon  vivid  backgrounds.  One  of  the  boxes  in  Milton- 
Bradley  's  Pseudoptics  contains  various  gray  and  colored 
rings  especially  adapted  to  the  demonstration  of  contrasts. 
Professor  Witmer's  Analytic  Psychology,  published  by 
Ginn  &  Co.  also  exhibits  contrasts  in  very  striking  forms. 

A  very  good  way  of  demonstrating  contrasts  is  to  set 
up  a  piece  of  colored  glass  so  that  the  light  from  a  window 
shall  fall  through  it  on  a  large  white  sheet  of  paper.  Be- 
tween the  colored  glass  and  the  sheet  of  paper  place  some 
object  which  will  cut  off  the  light  from  the  glass,  thus 


PSYCHOLOGICAL  EXPERIMENTS          59 

leaving  a  part  of  the  sheet  of  paper  illuminated  by  the 
general  diffuse  light  of  the  room.  This  uncolored  area  on 
the  paper  will  seem  by  contrast  with  the  general  field  in 
which  it  lies  to  be  colored  in  the  shade  complementary 
to  the  background. 

A  very  convenient  method  of  demonstrating  light  con- 
trasts is  to  prepare  a  disk  such  as  is  shown  in  Fig.  31,  A. 
This  disk,  it  will  be  seen,  has  around  the  center  a  complete 
circle  of  black.  In  successive  rings  toward  the  circum- 
ference of  the  disk  the  relative  amount  of  black  is  reduced, 
but  the  relation  of  black  and  white  in  each  ring  is  constant 
throughout  the  width  of  the  ring.  If  such  a  disk  as  this 


FIG.  31 


is  rotated  by  means  of  a  color  mixer,  there  will  be  pro- 
duced about  the  center  of  the  disk  one  black  ring,  and 
outside  of  this  a  series  of  gray  rings  differing  from  each 
other  in  intensity  in  such  a  way  that  each  succeeding  ring 
is  somewhat  lighter  than  that  which  lies  nearer  the  cen- 
ter. The  gray  rings  produced  during  rotation  will  not 
seem,  as  they  are  in  reality,  uniformly  gray  throughout 
their  widths.  That  part  of  each  ring  which  lies  nearest 
to  the  inner,  darker  ring  will  seem  relatively  light,  while 
that  part  of  the  ring  which  is  nearer  to  the  next  outer  ring 
will  seem  dark.  These  effects  are  due  to  contrast,  for 
wherever  a  gray  ring  is  in  immediate  contact  with  a  light 


60          LABORATORY  EQUIPMENT  FOR 

ring  it  will  seem  darker  and,  conversely,  where  it  is  in 
immediate  contact  with  the  darker  ring  it  will  seem  lighter. 

If  a  second  disk  is  prepared,  as  shown  in  Fig.  31,  B, 
with  fine  lines  drawn  between  the  successive  rings,  the 
contrast  effect  will  be  very  much  weakened  if  not  indeed 
entirely  destroyed.  The  lines  of  demarcation  between 
the  successive  rings  prevent  the  eye  from  traveling  freely 
across  from  one  ring  to  the  other  and  consequently  dis- 
turb the  contrast. 

Similar  disks  may  be  prepared  to  illustrate  color  contrast. 
Thus,  as  shown  in  Fig.  31,  C,  a  disk  may  be  prepared, 
the  outer  portion  of  which  is  blue,  the  inner  portion  of 
which  is  red.  If  now  between  these  two  large  portions 
of  the  disk  a  middle  ring  be  inserted  which  is  made  up  of 
one-half  of  blue  and  one-half  of  red,  there  will  be  produced 
when  rotation  begins  a  central  ring  of  purple.  This  cen- 
tral purple  will  seem  very  red  on  its  outer  circumference 
and  very  blue  on  its  inner  circumference,  because  at 
these  two  limiting  circumferences  contrast  with  the  neigh- 
boring field  is  pronounced. 

Reference  was  made  a  number  of  times  in  connection 
with  the  last  exercise  to  the  fact  that  the  eye  does  not 
respond  to  colors  in  the  same  way  after  it  has  been  for  a 
time  in  the  dark.  It  is  true  in  general  that  all  color  mix- 
tures and  color  contrasts  are  very  much  modified  by  a 
change  in  illumination.  The  general  principle  is  that 
the  reds  and  the  closely  related  colors  tend  to  disappear 
wherever  there  is  a  reduction  in  the  illumination,  before 
the  blues  and  closely  related  colors.  Consequently,  if  a 
mixture  is  made  of  red  and  blue  and  the  general  illumina- 
tion is  reduced,  the  mixture  will  show  a  stronger  blue 
quality  than  it  showed  in  the  stronger  intensity  of  light. 

The  third  supplementary  experiment  requires  that 
various  cases  of  color  experience  shall  be  compared  with 


PSYCHOLOGICAL  EXPERIMENTS          61 

each  other.  Such  comparison  can  be  made  by  matching 
each  experience  with  a  combination  of  standard  disks 
placed  in  a  constant  illumination.  Thus,  if  a  red  is  to  be 
compared  with  other  reds,  establish  in  each  case  an  equa- 
tion by  matching  the  first  red  with  a  combination  of 
standard  disks  and  expressing  the  combination  of  disks 
in  a  formula.  Then  find  the  formula  for  the  second  red 
and  so  on. 

The  best  method  of  demonstrating  the  difference  be- 
tween color  mixture  of  the  type  which  has  been  dealt  with 
in  this  exercise  and  the  type  of  mixture  which  is  involved  in 
combining  pigments,  is  to  prepare  a  disk  which  has  been 
covered  with  a  wash  of  pigments  in  the  following  manner: 
Let  the  outer  portion  of  the  disk  be  given  a  coat  of  blue 
over  half  of  its  surface.  Let  the  other  half  of  the  outer 
portion  of  the  disk  be  covered  with  yellow.  Let  the  inner 
portion  of  the  disk  be  painted  with  a  mixture  of  the  blue 
and  yellow  pigments.  The  result  of  mixing  these  two  pig- 
ments is  a  vivid  green.  If  the  disk  is  now  placed  upon  a 
color  mixer  and  rotated,  the  central  green  portion  will  not 
be  modified  in  any  way  by  the  fact  that  the  disk  is  ro- 
tated. The  outer  portion  of  the  disk  will,  on  the  other 
hand,  show  the  regular  complementary  relation  between 
blue  and  yellow;  that  is,  it  will  show  as  a  result  of  the  mix- 
ture a  decided  gray. 

After  thus  demonstrating  the  fundamental  difference 
between  pigment  mixing  and  mixing  by  the  method  of 
successive  stimulations,  the  nature  of  pigment  mixing 
may  be  explained  by  the  use  of  colored  glasses,  the  results 
of  such  a  test  being  exhibited  in  Fig.  32.  Set  up  in  a  ray 
of  sunlight  a  piece  of  blue  glass.  Examine  with  a  prism, 
or,  better,  with  a  spectroscope,  the  light  which  passes 
through  this  blue  glass.  It  will  be  found  that  the  glass 
has  deprived  the  white  light  of  most  of  the  red,  orange, 


62 


LABORATORY  EQUIPMENT  FOR 


and  yellow  components  which  it  originally  contained. 
The  blue,  green,  and  violet  components  of  the  white  light 
will  be  strong.  It  will  thus  he  seen  that  the  blue  color 
of  the  glass  is  due  to  the  fact  that  only  a  portion  of  the  orig- 
inal white  light  is  allowed  to  come  through  the  glass. 
Similarly,  it  will  be  found  on  examining  the  light  which 
comes  through  a  yellow  pane  of  glass  that  the  orange, 
yellow,  and  green  components  of  white  light  are  strong. 
There  is  a  great  reduction  in  intensity  of  the  reds,  blues, 


Yellow  Blue 

Fio.  32 

and  violets  by  the  yellow  glass.  If,  now,  light  which  has 
been  allowed  to  pass  through  the  yellow  glass  passes 
afterwards  through  the  blue  glass,  it  will  be  obvious  that 
only  that  color  which  passes  easily  through  both  glasses 
will  survive  the  double  process  of  absorption  through  the 
two  glasses.  The  rays  of  light  which  thus  pass  through 
both  kinds  of  glass  are  predominantly  green  in  quality. 
Whatever  other  rays  escape  absorption  are  so  completely 
submerged  by  the  strong  green  rays  that  the  light  seems  to 


PSYCHOLOGICAL  EXPERIMENTS          63 

be  altogether  green.  This  result  agrees  with  the  experi- 
ment of  mixing  yellow  and  blue  pigments  described  above. 
Indeed,  the  blue  and  yellow  pigment  particles  which  were 
used  in  making  the  color  washes  may  very  properly  be 
regarded  as  a  series  of  small  transparent  particles  of  blue 
and  yellow  media,  which  deprive  the  light  which  passes 
through  them  of  all  rays  except  the  green  rays  in  the  same 
way  that  yellow  and  blue  glass  would.  The  effect  of 
these  pigment  particles  is  due  to  the  fact  that  the  light 
which  falls  upon  the  surface  of  the  color  wash  is  carried 
downward  into  the  pigment  particles  for  a  certain  distance 
and  is  then  refracted  back  again  after  having  been  partially 
deprived  of  its  rays.  Combinations  of  pigments  other  than 
blue  and  yellow  can  be  worked  out  in  analogous  fashion. 
It  is  to  be  noted  in  general,  however,  that  most  other  pig- 
ments are  not  as  transparent  as  the  blue  and  yellow  pig- 
ments. There  is,  therefore,  in  general  a  great  reduction 
in  the  intensity  of  light  whenever  pigments  are  mixed 
with  each  other. 


EXERCISE  IV 

A  AND  B — APPARATUS,  PROCEDURE,  AND  RESULTS 

Exercise  IV  requires  very  little  apparatus.  The  head- 
rest which  was  described  on  page  32  may  again  be 
utilized  in  this  exercise,  or  the  simpler  devices  suggested 
in  the  same  exercise  will  serve.  The  eye  shield  is  de- 
scribed on  page  31.  The  measuring  rods  can  be  con- 
veniently held  in  clamps  of  the  kind  described  in  the 
general  statement  on  page  9.  In  measuring  distances 
on  the  rod  it  will  be  found  convenient  to  have  the  ex- 
perimenter move  some  bright  object,  like  a  strip  of  white 
card,  along  the  rod  until  it  seems  to  the  observer  to  be  in 
the  right  position  to  mark  the  boundary  of  the  object 
which  is  being  measured. 

Drawing  figures  to  scale  is  facilitated  by  the  use  of  sheets 
of  coordinate  paper.  This  renders  the  reduction  to  any 
desired  unit  very  easy.  Thus,  if  the  object  is  24  cm. 
long  and  12  cm.  wide  the  successive  measurements  will 
be  as  follows: 

At  3  M ....  18  cm.  long  by  9  cm.  wide 
At  2  M....12  cm.     "      "  6  cm.     " 
At  1  M....  6  cm.     "      "   3  cm.      " 

If  now  the  scale  chosen  for  the  drawing  on  the  coordinate 
paper  is  1mm.  =2  cm.,  the  length  and  width  of  the  object 
can  be  represented  by  two  lines  drawn  one  under  the  other, 
the  first  being  12  mm.  long,  the  second  being  6  mm.  long. 
Perpendicular  lines  should  then  be  drawn  from  the  centers 
of  each  of  these  lines  to  represent  the  distance  from  the 

64 


PSYCHOLOGICAL  EXPERIMENTS          65 

object  to  the  eye.  This  distance  will  be  represented  in 
the  figure  as  20  cm.  The  form  of  the  resulting  figure  is 
given  in  the  author's  Psychology,  General  Introduction, 
page  155. 

The  formula,  which  is  easily  derived  from  these  results, 
is  as  follows: 

}  (  to  the  corresponding  dimen- 

Any  dimension  f  .    .     ,,  , .    1    .          ,  . .  .     .? 

.  v      i  •          >  is  in  the  same  ratio  <  sion  of  its  projection  at  a 
of  the  omect     (  )  j-  A 

)  {  nearer  distance, 

(  the  distance  of  ^  (  distance  of  the 

as  <  the  object  from  >  is  to   the  <  projection  from 
(  the  eye  )  ( the  eye. 

The  diagram  and  calculation  can  be  directly  related  to 
the  image  on  the  retina  by  calculating  how  far  back  of 
the  optical  center  of  the  lens  the  rays  must  be  projected 
in  order  to  reach  the  retina.  In  any  given  case  the  dis- 
tance of  the  retina  from  the  optical  center  can  not  be  di- 
rectly determined,  but  a  general  average  of  many  eyes 
which  have  been  measured  justifies  the  general  assump- 
tion that  the  diameter  of  the  eye  is  23  mm.  and  that  the 
distance  of  the  optical  center  from  the  front  of  the  cornea 
is  7  mm.  The  full  formula  for  the  size  of  a  retinal  image 
is  accordingly: 

Dimen-  corresponding  distance  of  object 

sion  of     :      dimension    of       ::     from     front     of      :      16  mm. 

object  image  cornea  -f-  7  mm. 

An  excellent  exercise  for  a  class  is  to  require  the  compu- 
tation of  the  size  of  a  house  one  hundred  meters  distant 
which  seems  just  equal  in  height  to  one  cm.  held  at  a  dis- 
tance of  10  cm.  from  the  eye.  Also  give  the  size  of  the 
retinal  image  of  such  a  house.  How  large  would  the  ret- 


66          LABORATORY  EQUIPMENT  FOR 

inal  image  be  if  one  moved  away  to  twice  the  original 
distance  ? 

Turning  to  the  second  part  of  the  exercise,  a. well-de- 
fined after-image  may  be  secured  by  cutting  in  a  piece  of 
black  cardboard  a  cross  with  legs  about  ten  centimeters 
in  length  and  one  centimeter  in  width.  This  cross  should 
be  held  between  the  eye  and  the  bright  sky  and  the  ob- 
server should  look  steadily  at  one  point  on  the  cross  for 
a  minute.  If  the  cross  can  not  be  prepared,  a  gas  jet  or 
other  bright  object  gives  a  very  good  image. 

For  comparisons  of  the  apparent  sizes  of  projections  of 
the  after-image,  it  will  be  found  convenient  to  use  a  draw- 
ing-board on  which  has  been  tacked  a  sheet  of  paper 
marked  off  by  heavy  black  lines  into  square  decimeters. 
The  drawing-board  can  be  easily  moved  about  from  one 
position  to  others.  If  a  drawing-board  is  not  at  hand,  a 
similar  drawing  may  be  made  on  heavy  cardboard. 

The  formula  derived  above  will  be  found  to  hold  for 
all  of  the  distances  to  which  the  after-image  is  projected. 

It  may  be  found  necessary,  in  order  to  bring  out  the 
after-image  clearly  as  it  is  projected  to  the  various  posi- 
tions, to  wink  the  eyes  rapidly. 

The  Aubert's  diaphragm  required  for  the  third  part  of 
che  exercise  consists  of  two  pieces  of  metal  or  wood  each 
one  of  which  has  a  right  angle  notch  cut  in  one  end,  as 
indicated  in  Fig.  33,  1,  2  and  3,  4.  1,  2  may  now  be 
superimposed  upon  3,  4  to  any  desired  extent,  and  the 
result  will  always  be  a  symmetrical  diamond-shaped 
figure  1,  2,  3,  4.  This  Aubert's  diaphragm  should,  for 
the  purpose  of  the  experiment,  be  mounted  on  a  box. 
The  box  should  be  taken  into  a  dark  room  and  a  light 
should  be  placed  inside  of  the  box.  No  other  source  of 
light  should  be  present.  Between  the  light  and  the 
Aubert's  diaphragm  should  be  a  thick  plate  of  milk  glass 


PSYCHOLOGICAL  EXPERIMENTS 


67 


which  will  thoroughly  diffuse  the  light.  The  diaphragm 
will  control  the  size  of  this  diffusely  lighted  glass,  which 
is  the  only  object  in  the  room  visible  to  the  observer. 
In  addition  to  the  preparations  thus  far  described,  the 
box  should  be  mounted  on  runners  so  that  it  can  be  drawn 
backward  and  forward  in  the  third  dimension  directly 
in  front  of  the  observer.  Furthermore,  a  system  of  levers, 
represented  in  Fig.  33,  should  be  attached  to  the  parts  of 
the  diaphragm  so  as  to  permit  a  rapid  adjustment  of  the 
diaphragm  from  both  sides.  Lifting  the  long  handle  H 


FIG.  33 

produces  a  double  effect.  First,  it  throws  the  short  arm 
L,  which  is  rigidly  fastened  to  H,  outward  away  from  the 
center  of  the  diaphragm  opening.  The  part  of  the  dia- 
phragm 1,  2  is  drawn  outward  with  L,  for  L  is  fastened  to 
1,  2  by  means  of  a  pin  which  fits  into  a  slot  in  L.  The 
second  effect  produced  by  lifting  H  is  to  rotate  the  small 
cog-wheel  which  is  fastened  at  0,  the  center  of  movement 
in  H  and  L.  This  cog-wheel  in  turn  sets  in  motion  a 
second  similar  wheel  which  has  fastened  to  it  the  short 
lever  M,  at  P.  M  is  equal  in  length  to  L  and  is  fastened 
by  a  pin  and  slot  to  3,  4.  By  this  means  M  is  moved  in  a, 


68          LABORATORY  EQUIPMENT  FOR 

direction  opposite  to  L  whenever  H  is  lifted,  and  3,  4 
moves  in  -a  direction  opposite  to  1,  2.  When  //  is  moved 
downward  1,  2  and  3,  4  are  closed  in  on  each  other.  The 
advantage  of  the  whole  system  of  levers  is  that  the  center 
of  the  opening  always  remains  at  the  same  point,  and  the 
effect,  so  far  as  the  size  of  the  retinal  image  produced  by 
the  area  is  concerned,  is  the  same  as  the  effect  produced 
by  moving  the  area  in  a  direct  line  nearer  to  the  eye  or 
further  away. 

The  result  of  this  part  of  the  experiment  will  be  that 
the  observer  will  make  many  mistakes,  confusing  change 
in  distance  with  change  in  opening.  The  size  of  a  retinal 
image  will  thus  be  shown  to  be  complicated  with  interpre- 
tations of  distance  to  such  an  extent  that  size  and  distance 
must  be  recognized  as  closely  related  forms  of  interpre- 
tation. 

C — SUPPLEMENTARY   EXPERIMENTS 

The  first  supplementary  experiment  can  be  tried  in  a 
way  to  secure  an  accurate  record,  by  taking  a  piece  of 
cardboard  about  10  cm.  square  and  fixing  on  its  under 
surface  a  pin.  This  pin  should  not  be  allowed  to  perforate 
the  cardboard  but  should  be  fastened  wholly  on  the  under 
surface.  A  convenient  method  of  accomplishing  this  is  to 
pass  the  pin  through  a  small  piece  of  gummed  paper. 
When  the  pin  has  been  drawn  through  this  paper  as  far 
as  possible,  leaving  only  the  head  on  the  gummed  side  of 
the  paper,  the  whole  may  be  fastened  by  the  gum  to  the 
bottom  of  the  pasteboard.  The  pin  will  thus  be  held 
firmly  in  position  but  will  not  be  seen  on  the  upper  side 
of  the  pasteboard.  The  observer  should  now  hold  this 
pasteboard  with  the  pin  hanging  down  from  its  under 
side  at  the  level  of  his  open  eye,  the  other  eye  being  cov- 
ered or  closed.  Let  him  now,  by  means  of  a  lead  pencil, 


PSYCHOLOGICAL  EXPERIMENTS          69 

indicate  on  the  upper  surface  of  the  cardboard  the  point 
at  which  the  pin  seems  to  him  to  be  located.  A  number 
of  trials  can  be  easily  recorded  in  this  fashion  and  it  will 
be  found  that  the  distance  of  the  pin  from  the  eye  is  not 
accurately  observed.  After  this  let  him  make  the  same 
trials  with  both  eyes  open. 

The  reason  why  the  threads  required  for  the  second 
supplementary  experiment  described  in  the  Laboratory 
Manual,  should  be  enclosed  in  a  box  is  that  it  is  important 
to  exclude  shadows  and  to  cover  up  the  fastening  points 
of  the  threads.  Any  shadows  which  are  allowed  to  fall 
upon  the  threads  give  an  indication  of  the  differences  in 
position  of  the  differently  illuminated  threads.  Further- 
more, unless  some  device  is  employed  to  prevent  the 
observer  from  seeing  the  points  at  which  the  threads  are 
fastened,  he  will  be  able  to  judge  of  the  different  dis- 
tances of  the  threads  from  his  eyes  by  means  of  the  sur- 
faces which  lie  between  the  different  points  of  attachment. 
Let  threads,  preferably  of  different  sizes  and  of  different 
colors,  be  drawn  vertically  through  a  box  which  is  40  or 
50  cm.  cube.  Let  the  upper  and  lower  thirds  of  the  open- 
ing of  the  box  be  covered  with  gray  or  black  screens. 
The  observer  now  looks  through  the  middle  third  of  the 
box  and  observes  the  threads  which  lie  at  different  depths. 
He  will  be  able  to  designate  the  different  threads  by  their 
colors,  and  he  will  find,  if  he  looks  with  only  one  eye,  that 
it  is  almost  impossible  to  give  a  correct  judgment  of  their 
positions  in  the  third  dimension.  Professor  Jastrow  has 
arranged  a  demonstration  of  analogous  type  by  using 
cylinders  of  different  degrees  of  curvature.  A  variety 
of  blocks  of  wood  were  turned  with  different  diameters, 
and  these  were  placed  in  such  a  position  that  they  were 
not  covered  with  shadows  as  they  would  be  in  an  ordi- 
nary environment.  The  light  was  thrown  upon  them 


70 


LABORATORY  EQUIPMENT  FOR 


from  above.  The  result  was  that  when  they  were 
viewed  monocularly  it  was  found  to  be  very  difficult  to 
decide  which  one  had  the  greatest  degree  of  curvature. 

The  next  supplementary  experiment  will  give  the 
following  result.  When  the  pin-hole  is  held  very  near  to 
the  eye  it  is  inside  the  limit  for  near  accommodation  of 
the  lens.  The  result  is  that  the  light  coming  through  this 
pin-hole  will  not  be  focused  upon  the  retina  of  the  eye.  It 
will  come  to  a  theoretical  focus  behind  the  retinal  surface 
(Fig.  34,  F).  Since  it  is  not  focused  upon  the  retina  there 
will  be  an  area  of  diffuse  illumination  on  the  retinal  sur- 
face (Fig.  34,  RP).  The  lower  part  of  this  diffuse  area  will 


Fio.  34 

derive  its  light  directly  from  the  lower  part  of  the  pin- 
hole.  If,  now,  a  card  is  brought  between  the  pin-hole  and 
the  eye  and  is  gradually  drawn  upward  from  below  so 
as  to  cut  off  part  of  the  pin-hole,  it  will  obviously  cut 
off  first  those  rays  which  come  from  the  bottom  of  the 
pin-hole  (Fig.  34,  PP)  and  fall  upon  the  lower  part  of 
the  diffuse  circle  on  the  retina.  It  is  a  fact  of  general 
experience  that  all  rays  of  light  which  affect  the  lower  parts 
of  a  retinal  image  are  under  ordinary  circumstances  de- 
rived from  the  upper  parts  of  objects.  Put  in  other 
terms  it  may  be  said  that  the  direction  in  which  we  refer 
all  rays  of  light  falling  upon  the  retina  is  determined 


PSYCHOLOGICAL  EXPERIMENTS          71 

by  a  line  drawn  from  any  retinal  point  in  question  through 
the  optical  center  of  the  lens  (Fig.  34,  PW).  Under  the 
circumstances  of  this  experiment  to  interpret  the  lower 
part  of  the  retinal  image  as  related  to  the  upper  part  of  the 
object  is  misleading,  for  the  simple  reason  that  the  object 
has  not  been  brought  to  a  focus  upon  the  retina  as  are  the 
objects  seen  under  ordinary  conditions.  Thus,  as  seen 
in  Fig.  34,  the  light  PP  from  the  lower  part  of  the  pin-hole, 
and  the  light  RR  from  the  upper  part  of  the  pin-hole,  come 
to  the  theoretical  focus  F,  crossing  the  retina  at  the  points 
P  and  R.  The  image  will  be  interpreted  according  to  the 
ordinary  methods  of  interpreting  retinal  images  as  if 
PP  came  from  the  direction  VV  and  will  consequently  be 
regarded  as  coming  from  the  upper  part  of  the  figure,  the 
ray  of  light  affecting  R  being  interpreted  as  though  it  came 
along  the  axis  XX.  A  very  convenient  method  of  making 
this  demonstration  is  to  prepare  a  short  tube  about  4  cm. 
long,  one  end  of  which  is  entirely  closed  except  for  a  small 
pin-hole.  Directly  in  line  with  this  pin-hole  a  small  pin 
should  pass  through  the  wall  of  the  tube  in  such  a  way 
that  it  can  be  pushed  across  the  line  of  light  coming 
through  the  pin-hole. 

When  the  eye  moves  from  a  remote  object  to  a  point  near 
at  hand  the  observer  will  note  that  the  apparent  size  of 
the  remote  object  undergoes  a  change  such  that  it  seems 
to  be  somewhat  smaller  than  when  it  was  observed  di- 
rectly. If  the  new  center  of  fixation  is  the  finger  or  a  pen- 
cil held  near  the  face,  a  further  experiment  may  be  tried 
by  keeping  the  eye  fixed  upon  the  pencil  or  finger  as  it  is 
brought  nearer  and  nearer  to  the  eye.  During  this  move- 
ment of  the  center  of  fixation  toward  the  eye,  the  apparent 
size  of  the  remote  object  will  continue  to  grow  noticeably 
smaller.  An  explanation  which  has  sometimes  been 
offered  of  these  facts  is  that  the  finger  or  pencil  as  it  moves 


72    LABORATORY  EQUIPMENT  FOR 

toward  the  eye  gives  a  larger  and  larger  retinal  image, 
whereas  the  remote  object  continues  to  give  a  retinal  image 
of  the  same  size  as  at  first.  Since  the  finger  or  pencil  is 
the  more  clearly  seen  object  it  furnishes  a  standard  of 
estimation,  and  since  it  is  interpreted  as  constant  in  size 
in  spite  of  the  changes  in  the  retinal  image,  the  more  re- 
mote object  is  by  contrast  interpreted  as  growing  smaller. 
The  fatal  objection  to  this  explanation  is  that  exactly 
the  same  changes  in  apparent  size  in  the  remote  ob- 
ject appear  even  when  there  is  no  movement  of  the 
near  object.  Merely  looking  from  a  remote  object  to 
a  near  point  of  fixation  gives  the  result  that  the  remote 
object  seems  to  grow  smaller.  Indeed,  the  pencil  or  finger 
is  merely  a  device  for  securing  fixation  upon  a  point  near 
at  hand.  If  the  observer  is  capable  through  voluntary 
effort  of  fixating  the  eye  on  a  series  of  points  near  at  hand, 
he  can,  without  the  aid  of  a  pencil  or  finger,  secure  all  of 
the  results  described  above.  The  contrast  between  the 
near  object  and  the  remote  object  can  therefore  not  be 
the  explanation  of  the  facts  observed.  A  more  adequate 
explanation  can  be  given  by  assuming  that  the  center  of 
near  fixation  is  the  point  at  which  all  objects  in  the  field 
of  vision  seem  to  be  located;  that  is,  there  is  in  monocular 
vision  no  clear  discrimination  of  differences  in  depth. 
Consequently,  when  the  eye  fixates  a  near  point,  remote 
objects  seem  to  be  drawn  up  to  this  near  point.  Even  if 
there  is  some  suggestion  of  difference  in  depth  because  of 
shadows  or  other  secondary  characteristics,  yet  the  re- 
mote object  seems  to  be  nearer  to  the  point  of  fixation 
than  it  is  in  reality.  Since  the  retinal  image  from  the 
remote  object  is  constant  in  size  and  since  it  seems  to  fol- 
low the  movement  of  the  near  point  of  fixation,  it  will  be 
interpreted  as  growing  smaller  and  smaller  as  the  near 
point  of  fixation  approaches  the  eye.  This  experiment 


PSYCHOLOGICAL  EXPERIMENTS          73 

is  very  similar  to  the  experiment  described  above,  which 
dealt  with  the  projection  of  the  after-image,  and  the  prin- 
ciple of  interpretation  is  just  the  same. 

The  earliest  experiments  on  monocular  accommodation 
and  its  resulting  sensations  were  tried  by  means  of  threads 
suspended  in  front  of  the  observer.  A  uniform  gray 
surface  was  spread  out  before  the  observer  and  he  was  al- 
lowed to  look  at  this  uniform  surface  through  a  shield 
which  permitted  only  monocular  vision.  Across  this 
monocular  field  was  drawn  a  thread.  The  extremities  of 
the  thread  passed  out  of  the  field  of  vision  above  and  be- 
low. The  thread  was  now  moved  backward  and  forward 
and  the  observer  was  required  to  state  whenever  he  was 
able  to  distinguish  its  movement  in  depth  and  he  was  also 
required  to  state  the  direction  of  the  movement.  In  some 
cases  two  threads  were  used,  one  being  suddenly  replaced 
by  a  second  which  was  either  nearer  or  further  away  than 
the  first.  This  mode  of  experimentation  obviated  the 
necessity  of  pushing  the  single  thread  backward  and  for- 
ward, and  it  made  possible  more  sudden  changes  in  the 
position  of  the  thread. 

The  difficulty  with  this  whole  method  of  experimentation 
is  that  the  thread  in  spite  of  its  small  diameter  is  sufficiently 
large  to  give  an  appreciable  retinal  image.  When  now 
the  thread  is  moved  backward  and  forward,  its  retinal 
image  changes  in  size  according  to  the  general  laws  of 
visual  perspective.  This  change  in  size  constitutes  a 
secondary  criterion  which  may  be  used  by  the  observer  in 
judging  its  relative  position.  It  became  evident  in  the 
course  of  experimentation  that  a  method  should  be  de- 
vised by  which  some  sort  of  object  should  be  presented  in 
the  field  of  vision  that  could  be  moved  backward  and  for- 
ward without  changing  the  size  of  its  retinal  image. 
Such  an  object  can  be  produced  if  the  line  to  be  fixated 


74          LABORATORY  EQUIPMENT  FOR 

is  the  boundary  line  between  two  areas  in  the  field  of  vision. 
Since  the  boundary  line  is  a  geometrical  line  and  has  no 
width  it  will  not  change  in  width  as  it  is  moved  backward 
and  forward.  If  this  line  is  made  long  enough  so  that  it 
always  extends  through  the  whole  field  of  vision  in  the 
vertical,  it  will  obviously  not  change  in  apparent  length. 
The  method  of  producing  such  a  line  is  as  follows:  Let 
a  uniformly  illuminated  field  be  set  up  in  a  dark  room. 
The  illumination  of  this  field  may  be  either  from  shielded 
lamps  which  throw  their  light  only  upon  the  gray  surface 
leaving  other  objects  in  the  room  dark,  or  by  means  of  a 
plate  of  milk  glass  which  is  illuminated  from  behind.  At 
a  suitable  distance  in  front  of  this  illuminated  field  the 
observer  is  placed  behind  a  screen  through  which  he  can 
look  with  only  one  eye.  Such  a  screen  as  this  should 
usually  be  provided  with  a  tube  through  which  the  ob- 
server must  look.  The  tube  serves  better  than  a  single 
opening  in  the  shield  to  limit  the  field  of  monocular  vision 
so  as  to  exclude  all  of  the  objects  in  the  room  except  a  por- 
tion of  the  uniformly  lighted  field.  Half  way  across 
this  circular  monocular  field  of  vision  is  projected  a  black 
screen  with  a  sharp  edge.  This  black  screen  should  not 
be  lighted  at  all  on  the  side  which  is  turned  toward  the 
observer.  Since  it  cuts  off  one  part  of  the  observer's 
field  of  vision  it  leaves  only  a  part  of  the  former  circular 
field  visible,  and  gives  a  sharply  defined  line  between  the 
black  field  and  the  gray  semicircular  surface.  If  now 
this  black  shield  is  moved  backward  and  forward,  the 
boundary  line  between  the  black  and  light  portions  of  the 
monocular  field  will  constitute  an  object  of  invariable 
dimensions.  The  ability  of  the  observer  to  recognize 
the  position  of  this  boundary  line  can  be  measured  exactly, 
as  in  earlier  experiments  his  ability  to  recognize  the  posi- 
tion of  the  thread  was  measured,  by  determining  the 


PSYCHOLOGICAL  EXPERIMENTS          75 

distance  through  which  the  line  must  be  moved  in  order 
that  its  change  in  position  shall  be  recognized. 

There  is  one  criticism  to  be  made  of  certain  of  the  inter- 
pretations which  have  been  given  to  the  results  of  these 
experiments.  It  has  sometimes  been  assumed  that  the 
covered  eye  is  excluded  as  a  source  of  sensation  and  that 
the  experiment  deals  with  purely  monocular  phenomena. 
The  fact  is  that  the  closed  eye  exercises  in  many  ways  a 
large  influence  upon  the  open  eye.  Indeed,  in  certain  in- 
dividuals it  has  been  shown  that  the  kind  and  degree  of 
influence  exercised  by  the  closed  eye  introduces  very  com- 
plex factors  into  the  total  situation.  Thus,  it  has  been 
shown  that  there  is  in  some  cases  a  tendency  for  the 
closed  eye  to  relax  somewhat  in  its  muscular  tensions  and 
to  take  a  position  somewhat  divergent  from  that  which 
it  would  assume  if  it  were  open  and  fixating  the  same  ob- 
ject as  the  uncovered  eye.  On  the  other  hand,  while  there 
is  some  tendency  toward  divergence  in  the  covered  eye, 
there  is  unquestionably  a  tendency  for  this  eye  to  fixate 
the  same  point  as  does  the  uncovered  eye.  All  these 
tendencies  of  movement  contribute  sensory  factors  and 
also  complicate  the  behavior  of  the  open  eye,  as  has  been 
amply  shown  by  photographic  records  of  the  eye's  move- 
ment. 

A  great  deal  of  experimentation  was  undertaken  in  the 
early  years  of  experimental  psychology  to  determine  the 
minimum  visibile  or  least  recognizable  distance  between 
two  points.  The  simplest  method  of  making  this  deter- 
mination was  to  draw  two  points  or  two  parallel  lines  upon 
a  sheet  of  paper  and  gradually  move  this  paper  further 
and  further  away  from  the  observer.  As  the  points  were 
moved  further  and  further  away  the  retinal  image  of  the 
intervening  space  gradually  decreased  in  size  until  finally 
the  two  images  seemed  to  flow  together.  The  size  of  the 


76          LABORATORY  EQUIPMENT  FOR 

image  could  now  be  computed  by  the  formula  given  on 
page  65.  By  this  method  it  was  shown  very  clearly  that 
the  least  perceptible  distance  between  points  or  lines 
when  seen  in  direct  vision  is  very  much  less  than  the  least 
perceptible  distance  between  points  or  lines  which  are 
seen  indirectly.  The  just  perceptible  distance  is  in- 
fluenced in  a  measure  by  the  amount  of  illumination. 
If  the  experiment  is  made  by  drawing  black  lines  on  a 
white  sheet  of  paper  and  the  white  sheet  of  paper  is  rela- 
tively little  illuminated,  the  lines  will  flow  together  much 
sooner  than  they  will  when  the  paper  is  brilliantly  illu- 
minated ;  that  is,  the  intervening  white  space  in  such  a  case 
will  be  recognized  much  longer  when  it  has  a  high  light 
intensity  than  when  it  is  very  faint.  It  is  probably  true 
that  if  an  intermediate  area  were  illuminated  with  suffi- 
ciently great  brilliancy  it  would  never  disappear  between 
two  bounding  dark  surfaces.  Standard  illumination  is 
therefore  quite  as  essential  to  the  success  of  this  experi- 
ment as  any  other  condition. 

The  value  of  such  experiments  as  these  is  very  largely 
that  they  determine  the  acuity  of  the  organ  of  sense.  The 
importance  of  the  results  is  that  they  throw  light  on  the 
general  problem  of  the  differentiation  of  sensory  surfaces. 
Since  the  tests  are  of  value  chiefly  in  determining  the  con- 
dition of  the  organ  of  sense  they  have  been  worked  out  in 
a  much  more  practical  form  by  those  who  are  constantly 
called  upon  to  use  them  for  diagnostic  purposes.  The 
oculists  have  devised  a  number  of  methods  for  testing 
the  acuity  of  vision.  Charts  made  up  of  letters  of  differ- 
ent sizes  are  commonly  utilized  to  test  vision.  These 
charts  are  placed  in  a  given  illumination  and  the  ob- 
server is  tested  with  reference  to  his  ability  to  read  the 
different  sized  letters.  The  greater  the  acuity  of  vision 
the  smaller  the  letters  which  he  will  be  able  to  recognize. 


PSYCHOLOGICAL  EXPERIMENTS          77 

These  visual  charts  have  been  modified  sometimes  in 
order  to  adapt  them  to  use  with  illiterate  persons.  In- 
stead of  letters,  lines  drawn  in  such  relation  as  to  consti- 
tute the  three  sides  of  a  rectangle  are  placed  in  various 
positions.  Thus  the  open  side  of  the  rectangle  is  some- 
times placed  above,  sometimes  below,  sometimes  at  the 
right,  and  sometimes  at  the  left.  The  observer  is  required 
to  indicate  which  side  of  the  figure  is  open.  These  figures 
are  printed  in  various  sizes  upon  the  chart,  and  the  acuity 
of  vision  is  tested  by  the  observer's  ability  to  recognize 
correctly  the  figures  at  standard  average  distances. 


EXERCISE  V 


A  AND  B — APPARATUS,  PROCEDURE,  AND  RESULTS 

The  student  after  observing  double  images,  as  directed 
in  the  Laboratory  Manual,  should  represent  the  relations 
involved  by  means  of  a  diagram. 

Fig.  35  represents  the  relation  between  the  two  eyes 
and  the  two  objects  N  and  R,  which  are  located  at  different 
distances  in  depth  from  the  observer.  Rays  of  light  from 
N  passing  through  the  optical  centers  of  the  lenses  of  the 


Fio.  35 

two  eyes  pass  to  the  points  F  and  Ff,  which  represent  the 
two  foveas  in  the  two  eyes.  The  fact  that  the  images 
from  N  fall  on  the  foveas  indicates  that  the  two  eyes  are 
fixating  this  near  point.  The  rays  of  light  from  the  re- 
mote point  R  will  also  pass  through  the  optical  centers 
of  the  lenses  and  will  fall  upon  the  two  retinas  at  the 
points  R  and  R'.  It  will  be  noted  that  R  and  Rf  are  both 
on  the  nasal  sides  of  the  retinas.  Any  point  other  than 

78 


PSYCHOLOGICAL  EXPERIMENTS          79 

the  point  of  fixation,  if  at  the  same  depth,  casts  its  image 
on  the  retinas  of  the  two  eyes  in  such  positions  that  in 
one  eye  the  image  will  fall  on  the  temporal  side  of  the  fovea 
and  in  the  other  eye  on  the  nasal  side  of  the  fovea.  The 
condition  which  is  represented  in  Fig.  35  is  therefore  one 
in  which  fusion  of  the  two  images  can  not  follow  as  it 
would  under  ordinary  conditions  of  observation  of  plane 
surfaces.  The  two  retinal  images  R  and  R',  falling  both 
on  the  nasal  sides  of  the  two  retinas,  do  not  fuse.  The 
observer  will  consequently  see  these  two  images  as  separate. 
Some  observers  have  difficulty  in  recognizing  such  double 
images.  This  is  due  to  the  fact  that  objects  not  in  the 
center  of  the  field  of  vision  are  vague  because  they  are  not 
clearly  focused,  and  they  are  consequently  for  the  most 
part  neglected.  Furthermore,  there  are  a  great  many 
observers  who  habitually  neglect  to  a  greater  or  less  de- 
gree one  of  their  retinal  images.  If  the  double  images 
R  and  R'  are  recognized  as  separate  by  the  observer,  it  will 
be  further  noted  that  the  image  for  the  left  eye  appears  to 
lie  on  the  left  side  of 'the  point  of  fixation.  This  can  be 
clearly  demonstrated  by  closing  or  covering  the  left  eye. 
Correspondingly,  the  image  for  the  right  eye  will  seem  to 
lie  on  the  right  side  of  the  center  of  fixation.  Under 
these  conditions  the  double  images  are  called  uncrossed 
double  images. 

If  the  same  diagram  is  used  to  represent  the  reversed 
condition  where  the  eyes  are  fixated  upon  the  more  re- 
mote object  R,  the  points  R  and  R'  must  be  treated  as  the 
two  foveas.  F  and  Ff  will  therefore  represent  two  points 
on  the  temporal  sides  of  the  retinas.  These  images  will 
be  seen  as  double  and  will  seem  to  lie  on  sides  of  the 
center  of  fixation  exactly  opposite  from  the  eyes  to  which 
they  belong;  that  is,  the  image  for  the  right  eye  will  seem 
to  lie  on  the  left  side  of  the  center  of  fixation  and  the  image 


80          LABORATORY  EQUIPMENT  FOR 

for  the  left  eye  will  seem  to  lie  on  the  right.  These  double 
images  are  known  as  crossed  double  images. 

The  clearest  explanation  of  the  apparent  position  of 
these  double  images  is  that  the  objects  not  at  the  center  of 
fixation  are  attracted  toward  the  center  of  fixation,  as  in- 
dicated in  an  earlier  exercise,  page  72.  The  points 
where  the  lines  of  light  from  the  objects  cross  the  plane 
of  the  point  of  fixation  will  accordingly  determine  the  ap- 
parent position  of  the  double  images  in  space.  In  Fig. 
35  the  planes  are  represented  by  two  lines  00'  and  SS'. 
If  the  center  of  fixation  is  the  near  point,  the  lines  of  light 
from  the  more  remote  object  cross  the  nearer  plane  at 
the  points  0  and  0'.  If  the  center  of  fixation  is  the  more 
remote  object,  the  lines  of  light  from  the  near  points  must 
be  projected,  as  indicated  in  the  dotted  lines,  to  the  re- 
mote plane,  which  they  will  intersect  at  the  points  S  and 
<S'.  Double  images  are  essentially  monocular  phenom- 
ena. They  appear  in  the  binocular  field  but  they  are  due 
to  an  absence  of  fusion  of  the  images.  They  can  be 
studied  with  reference  to  their  characteristics,  and  it  will 
be  found  in  general  that  they  do  not  give  data  necessary 
for  localization  in  depth. 

A  very  good  introduction  to  the  second  part  of  Exercise 
V  is  to  require  the  student  to  indicate  by  means  of  a  dia- 
gram the  form  and  position  of  the  images  on  the  retinas 
of  the  two  eyes  from  a  solid  object.  (See  Psychology, 
Gen.  Intr.,  page  159,  Fig.  48.)  The  student  should  also 
draw  a  similar  figure  indicating  the  character  of  the  retinal 
images  derived  from  a  hollow  object. 

Any  solid  object  will  serve  to  show  the  difference  be- 
tween the  images  of  the  right  and  left  eyes.  It  is  desirable, 
however,  that  the  object  observed  be  small  enough  and 
simple  enough  so  that  the  student  can  draw  it  for  the  later 
parts  of  the  experiments,  hence  the  suggestion  of  a  trim- 


PSYCHOLOGICAL  EXPERIMENTS 


81 


cated  pyramid.  Small  blocks  of  wood  should  be  sawn 
out  with  a  square  base  of  5  cm.  on  each  side.  The  pyra- 
mid should  be  from  4  to  6  cm.  in  height  and  the  small 
truncated  surface  at  the  top  of  these  models  should  be 
2  cm.  on  each  side.  The  figure  will  be  much  more  easily 
used  for  the  purposes  of  making  drawings  if  the  surfaces 
of  the  block  are  painted  black  and  the  edges  are  marked 
with  a  fine  white  line.  The  observer  should  now  set  this 
model  on  a  piece  of  paper  and  should  close  one  eye  and 
examine  the  model  with  the  single  open  eye.  He  should 
indicate  by  points  on  the  paper,  first  the  dimensions  of 


FIG.  36 

the  base,  and  then  the  apparent  position  of  the  edges  of 
the  small  upper  surface  when  this  is  projected  to  the  plane 
of  the  paper.  Without  changing  the  position  of  his  head, 
let  him  now  open  the  eye  which  a  moment  before  was 
closed  and  close  the  eye  which  was  open.  Again,  let  him 
plot  the  dimensions  of  his  figure  on  the  paper,  noting 
especially  the  change  in  the  apparent  position  of  the  pro- 
jection of  the  upper  square.  He  should  now  draw  the 
figure  in  full  with  a  result  similar  to  that  shown  in  Fig. 
36,  where  A  is  the  image  for  the  left  eye,  B  the  image  for 
the  right  eye. 
The  next  step  of  the  experiment  consists  in  preparing 


82 


LABORATORY  EQUIPMENT  FOR 


the  apparatus  for  the  fusion  of  these  two  figures.  The 
apparatus  in  its  simplest  form  is  a  mirror  stereoscope. 
Let  two  boards  be  set  up  as  indicated  in  Fig.  37,  1  and  2. 
These  boards  are  held  most  firmly  in  position  by  means 
of  a  common  base  BB.  On  the  base  BB  should  be  set  up 
two  mirrors  placed  at  angles  of  45°  with  reference  to 
1  and  2,  and  at  an  angle  of  90°  with  respect  to  each  other. 
Rays  of  light  from  board  1  will  now  be  reflected  forward 
from  the  mirror  3,  while  rays  of  light  from  board  2  will  be 
reflected  by  the  mirror  4.  If  the  two  eyes  of  the  observer 


FIG.  37 

are  placed  so  as  to  look  into  mirrors  3  and  4,  the  observer 
will  see  the  rays  of  light,  which  in  reality  come  from  the 
boards  1  and  2,  as  if  they  came  from  some  point  in  space 
behind  the  mirrors.  If,  now,  instead  of  plain  boards 
1  and  2,  the  figures  drawn  from  the  truncated  pyramid 
are  placed  in  proper  position  on  these  boards,  the  observer 
will  see  the  images  as  if  they  came  from  a  single  object  be- 
hind the  mirrors  and  will  fuse  them  into  a  single  figure  in 
space.  Fig.  38  shows  the  fusion  in  diagrammatic  outline. 


PSYCHOLOGICAL  EXPERIMENTS 


83 


A  stereoscope  of  this  form  can  be  set  up  without  any 
special  construction  of  new  parts  if  the  laboratory  is  sup- 
plied with  a  sufficient  variety  and  number  of  clamps  and 
rods. 

The  mirror  stereoscope  suffers  from  certain  defects 
which  interfere  somewhat  with  its  use.  In  the  first  place, 
any  ordinary  mirror  has  three  reflections  from  its  surfaces. 
One  reflection  comes  from  the  upper  surface  of  the  glass, 
a  second  from  the  lower  surface,  and  a  third  from  the  silver 
surface.  The  latter  two  images  are  so  near  each  other  that 


they  do  not  interfere  noticeably  with  the  experiment. 
The  image  from  the  outer  surface  of  the  glass,  however, 
will  disturb  the  ordinary  observer  very  decidedly.  There 
is  no  easy  method  of  obviating  this  difficulty.  A  method 
which  may  be  adopted  consists  in  securing  highly  polished 
metal  surfaces  and  using  these  for  mirrors.  Such  metallic 
mirrors  are,  however,  likely  to  tarnish,  and  it  is  difficult 
to  keep  them  ready  for  use.  A  better  expedient,  if  one 
is  conveniently  near  a  mirror-manufacturing  establish- 
ment, is  to  secure  small  mirrors  before  the  silver  surface 


84          LABORATORY  EQUIPMENT  FOR 

used  on  the  back  of  the  glass  has  been  covered  with  paint, 
as  it  is  in  the  finished  mirror.  The  silver  surface  which  is 
intended  for  use  through  the  glass  may  be  used  in  such 
unfinished  mirrors  on  the  side  turned  away  from  the  glass, 
provided  the  mirror  is  carefully  handled.  From  this 
unfinished  surface  only  one  reflection  will  be  received. 
Such  a  mirror  tarnishes  very  soon  and  can  not  be  re- 
newed without  destroying  the  silver  surface  altogether. 
A  new  mirror,  must,  therefore,  be  provided  for  each  series 
of  experiments.  A  second  limitation  of  the  mirror  stereo- 
scope consists  in  the  fact  that  it  neglects  a  natural  habit 
of  adjustment  which  appears  in  all  observers.  In  general 
it  is  true  that  the  lenses  in  the  two  eyes  are  habitually  ad- 
justed in  focus  to  the  point  of  fixation;  that  is,  if  the  two 
eyes  are  converged  upon  a  point  one  meter  distant  from 
the  eyes,  the  lenses  will  be  so  accommodated  as  to  focus 
light  which  comes  from  the  distance  of  one  meter.  This 
type  of  adjustment  very  often  does  not  suit  the  conditions 
presented  by  the  mirror  stereoscope.  Thus,  if  the  center 
upon  which  the  eyes  are  converged  in  looking  at  the  stereo- 
scopic object  lies  at  a  certain  distance  back  of  the  two  mir- 
rors, the  lenses  may  very  frequently  be  called  upon  to 
focus  light  which  comes  from  a  distance  very  different  from 
that  of  the  point  of  convergence,  because  the  light  which 
enters  the  eye  originates  from  the  figures  tacked  to  the 
boards  of  the  stereoscope  rather  than  from  the  point  of  fix- 
ation. The  only  condition  under  which  the  natural  ad- 
justments are  the  proper  adjustments,  are  those  under 
which  the  center  upon  which  the  two  eyes  are  converged 
is  at  exactly  the  same  distance  from  the  eyes  as  the  figures 
from  which  the  images  on  the  two  retinas  are  derived.  In 
order  that  this  particular  case  may  be  attained,  it  is  de- 
sirable that  the  simple  form  of  stereoscope  described  above 
be  elaborated  so  as  to  make  the  distance  of  the  images 


PSYCHOLOGICAL  EXPERIMENTS          85 

from  the  two  eyes  variable.  This  can  be  done  either  by 
making  the  boards  1  and  2  (Fig.  37)  adjustable  in  their 
distance  from  the  mirrors  or  by  making  the  angle  between 
the  two  mirrors  adjustable.  An  adjustment  of  the  two 
boards  1  and  2  can  be  provided  for  by  mounting  these 
boards  on  wooden  blocks,  which  in  turn  fit  into  runners 
placed  along  the  base  of  the  stereoscope,  BB. 

The  mirrors  3  and  4  may  also  be  mounted  upon  separate 
standards  so  as  to  be  adjustable  in  their  angle  with  refer- 
ence to  each  other.  In  an  even  more  elaborate  form  of 
apparatus,  the  base  BB  is  divided  into  halves  and  so 
mounted  that  each  half  can  be  rotated  about  a  single  point 
between  the  two  mirrors.  In  this  way  the  angle  of  the 
mirrors  with  reference  to  each  other  can  be  changed 
without  disturbing  the  relative  angular  positions  of  draw- 
ings 1  and  2  with  reference  to  their  respective  mirrors. 
Experiments  may  in  this  way  be  made  on  movements  of 
convergence  without  disturbing  the  other  relations  in- 
volved, especially  those  between  the  figures  tacked  to  1 
and  2  and  the  mirrors  which  reflect  their  images. 

The  mirror  stereoscope  may  be  made  in  almost  any 
desired  dimensions.  A  very  convenient  size  is  one  in 
which  the  base  BB  is  1  meter  long  and  25  cm.  wide.  The 
mirrors  in  such  an  apparatus  should  be  5  cm.  square. 
Smaller  stereoscopes  may  be  made  to  give  excellent  results. 
The  figures  must,  however,  in  such  cases  be  made  much 
smaller,  and  the  student  can  not  deal  as  easily  with  models 
in  preparing  the  figures  to  be  fused. 

If  the  two  drawings  represented  in  Fig.  36  are  fused  in 
the  stereoscope,  the  result  will  be  that  the  observer  will  see 
a  single  solid  truncated  pyramid  all  sides  of  which  are  sym- 
metrical. If,  now,  the  wide  side  of  one  of  the  figures  is 
covered,  the  fused  figure  of  the  pyramid  will  change  some- 
what in  its  character.  It  will  no  longer  seem  to  be  a  sym- 


86          LABORATORY  EQUIPMENT  FOR 

metrical  figure,  nor  will  the  side  which  is  now  seen  monocu- 
larly  be  solid  as  in  the  original  fused  figure.  There  will 
be  a  continuous  outline  of  the  pyramid  on  the  side  for 
which  one  figure  is  covered,  but  this  side  will  seem  flat, 
and  since  it  is  the  wide  side  of  one  of  the  drawings  which 
was  covered  the  figure  seen  will  seem  narrow.  Con- 
versely, if  the  narrow  side  of  the  figure  is  covered,  the  cor- 
responding part  of  the  pyramid  will  seem  flat  and  wide. 
The  fact  that  the  monocularly  seen  parts  of  the  pyramid 
are  respectively  too  narrow  and  too  wide  shows  that  the 
binocularly  seen  figure  has  a  width  which  is  a  compromise 
between  the  width  of  the  two  monocular  figures.  When 
both  the  wide  and  narrow  sides  are  present,  they  give 
through  fusion  a  compromise  width,  and  they  also  yield 
the  characteristic  of  solidity  which  was  not  present  in  either 
of  the  monocular  elements  which  entered  into  the  total 
figure.  These  observations  give  the  clearest  evidence  that 
the  fusion  process  is  one  in  which  all  of  the  sensory  factors 
receive  due  recognition,  the  resultant  characteristics  of  the 
binocular  figure  depending  upon  compromises  and  fusions 
of  the  monocular  elements.. 

Two  figures  with  no  lines  in  common  can  easily  be  pre- 
pared for  the  last  part  of  this  exercise  by  drawing  on  one 
card  a  series  of  vertical  lines  and  on  the  other  a  series  of 
horizontal  lines.  When  the  effort  is  made  to  fuse  these 
two  groups  of  lines  the  observer  will  see  first  one  set  of 
lines  and  then  the  other.  In  some  cases  the  lines  will  not 
appear  and  disappear  as  a  single  group,  but  there  will 
be  a  small  area  at  which  the  vertical  lines  will  appear 
in  the  midst  of  a  horizontal  field,  and  this  area  of 
vertical  lines  will  gradually  spread  until  the  horizontals 
are  for  the  most  part  submerged.  Other  figures  can  be 
prepared  by  using  lines  which  extend  in  various  direc- 
tions. Surfaces  of  different  colors  may  also  be  useq  to 


PSYCHOLOGICAL  EXPERIMENTS 


87 


show  the  lack  of  complete  fusion  between  entirely  different 
kinds  of  fields. 


C — SUPPLEMENTARY   EXPERIMENTS 

The  stroboscope  is  an  apparatus  by  means  of  which 
there  is  exposed  to  the  eye  of  the  observer  a  rapid  succession 
of  figures.  These  figures  represent  the  successive  stages 
of  some  activity,  such  for  example  as  the  flight  of  a  bird  or 
the  movements  of  an  animal  or  human  being  in  walking 
or  running.  The  essential 
condition  for  successful 
fusion  of  such  a  series  of 
figures  is  that  the  eye  shall 
see  one  image  for  an  in- 
stant and  shall  then  be 
supplied  with  an  entirely 
different  image,  the  first 
being  covered  so  as  to 
avoid  any  blurring  or  fu- 
sion of  the  two  successive 
images.  The  stroboscope  FIG.  39 

is  usually  made  in  the  form 
of  a  cylindrical  case  in 
which  a  succession  of  vertical  slits  are  cut.  (For  a 
simple  hand  stroboscope  see  Fig.  39.)  Back  of  each 
of  these  slits  is  introduced  a  single  figure.  When  now 
the  eye  looks  through  one  of  these  slits  it  sees  the  single 
figure  which  lies  behind  it.  As  the  cylinder  is  rotated 
this  image  is  cut  off  after  being  seen  by  the  observer,  and 
as  a  new  slit  comes  before  the  eye  a  second  image  is  ex- 
posed to  view,  and  so  on. 

A  recent  observer  has  described  a  very  interesting  ex- 
periment, in  which  by  means  of  the  stroboscope  the  suc- 


From  the  catalogue  of  M.  Kohl, 
Chemnitz,  Germany 


88          LABORATORY  EQUIPMENT  FOR 

cessive  views  of  a  solid  object,  which  would  be  seen  by 
looking  at  the  object  with  a  single  eye  first  on  the  right  side, 
then  from  directly  in  front  and  finally  from  the  left  side, 
are  fused  when  viewed  successively  in  the  stroboscope  in 
such  a  way  as  to  give  the  appearance  of  solidity.  There 
can  be  no  doubt  that  a  person  who  has  only  one  eye  de- 
rives from  his  head-movements  a  series  of  images  from 
solid  objects  which  he  uses  for  the  recognition  of  solidity 
in  a  way  very  similar  to  that  in  which  the  normal  indi- 
vidual uses  binocular  differences. 

An  elaborate  apparatus  which  is  in  principle  the  same  as 
the  stroboscope  is  familiar  to  all  who  have  seen  the  mov- 
ing pictures  or  kinetoscope  pictures  which  are  commonly 
used  to  reproduce  series  of  movements.  The  kinetoscope 
uses  a  series  of  photographs  which  correspond  to  the  differ- 
ent stages  of  the  movement  to  be  represented  and  pro- 
jects these  photographs  in  rapid  succession  upon  the  same 
point  on  the  screen. 

When,  as  suggested  in  the  second  supplementary  ex- 
periment, the  angle  between  the  two  mirrors  is  changed, 
the  center  of  convergence  for  the  two  eyes  will  move  in- 
ward or  outward — inward  if  the  angle  of  the  mirrors  with 
respect  to  each  other  is  decreased,  and  outward  whenever 
the  angle  is  increased.  The  angles  through  which  the 
mirrors  may  be  rotated  are  small.  If  these  angles  are 
made  too  large,  fusion  of  the  two  images  ceases  and  double 
images  appear.  With  every  change  in  the  degree  of 
convergence  there  will  come  a  distinct  perception  of  change 
in  position  of  the  object.  There  will  also  result  a  percep- 
tion of  change  in  size  such  that  the  object  will  seem  to 
grow  smaller  if  the  angle  of  the  mirrors  is  decreased  and 
the  point  of  fixation  is  made  to  approach  the  observer, 
while  the  object  will  seem  to  -grow  larger  if  the  angle  be- 
tween the  mirrors  increases  and  the  point  of  fixation  re- 


PSYCHOLOGICAL  EXPERIMENTS          89 

cedes.     If  the  changes  here  under  discussion  are  extreme, 
double  images  will  result,  as  indicated  above. 

Certain  of  the  effects  produced  by  changing  the  angles 
of  the  mirrors  can  be  paralleled  by  simple  experiments 
with  natural  objects  when  these  are  viewed  in  adjustable 
mirrors.  Let  two  mirrors  be  held  in  exactly  the  same  plane 
as  shown  in  the  full  drawn  lines  A,  B,  in  Fig.  40,  and  let 
some  object  0  be  observed  at  0 i  as  it  is  reflected  in  these 


FIG.  40 


two  mirrors.  The  apparent  distance  of  the  object  from 
the  observer  will  be  equal  to  the  total  distance  through 
which  the  light  has  traveled  from  the  object  to  the  eye; 
that  is,  it  will  seem  to  be  as  far  behind  the  mirrors  as  the 
object  is  in  reality  in  front  of  the  mirrors.  If,  now,  the 
two  mirrors  are  so  arranged,  as  indicated  at  A  and  B  in 
Fig.  40,  that  the  reflected  rays  which  enter  the  right  eye 
come  from  the  right-hand  mirror,  while  the  reflected 


90 


LABORATORY  EQUIPMENT  FOR 


rays  entering  the  left  eye  come  from  the  left-hand  mirror, 
the  angle  of  convergence  can  be  modified  without  modi- 
fying the  actual  distance  through  which  the  light  travels. 
This  can  be  done  by  changing  slightly  the  angle  between 
the  two  mirrors,  as  indicated  by  the  broken  lines  L  and 
D  in  Fig.  40.  Since  the  lines  of  convergence  are  changed 
by  this  inclination  of  the  mirrors,  the  point  of  fixation 
will  also  seem  to  change,  coming  to  the  point  O2,  and  there 


Fir,.  41 

will  result  an  apparent  modification  in  the  position  and 
size  of  the  object.  The  apparent  change  in  position  will 
follow  the  rule  that  whenever  the  angle  between  the  two 
mirrors  on  the  side  of  the  observer  is  greater  than  180°, 
the  object  will  seem  to  approach  and  at  the  same  time  to 
grow  smaller.  Whenever  the  angle  on  the  side  of  the  ob- 
server is  less  than  180°,  the  object  will  seem  to  recede  and 
grow  larger.  Only  very  small  changes  in  the  angle  can 


PSYCHOLOGICAL  EXPERIMENTS          91 

be  made  without  producing  double  images.    The  angle 
shown  in  the  figure  is  much  exaggerated. 

The  third  supplementary  experiment  requires  the  use 
of  the  pseudoscope.  The  simplest  form  of  pseudoscope  is 
one  which  was  devised  by  Prof.  George  M.  Stratton.  It 
consists  of  a  box,  as  represented  in  Fig.  41,  which  is  sup- 
plied with  three  openings  a,tA,B,  and  L.  The  distance  be- 
tween A  and  B  and  between  B  and  L  should  be  about  the 
ordinary  distance  between  the  two  eyes  of  an  observer; 
namely,  between  5  and  7  cm.  In  order  to  make  the  box 
useful  for  a  great  number  of  observers,  the  holes  at  A,  B, 
and  L  should  be  made  in  the  form  of  ellipses  about  1  cm. 
in  the  transverse  axis  and  2  cm.  in  the  axis  lying  in  the 
line  of  the  three  holes.  In  front  of  the  hole  B  should  be 
mounted  a  mirror,  as  indicated  at  M ,  at  an  angle  of  45° 
from  the  back  of  the  box.  A  second  mirror  should  be 
mounted  at  M'  in  the  corner  of  the  box  parallel  to  the 
mirror  M.  If  now  the  two  eyes  of  the  observer  are  brought 
into  position  before  the  openings  A  and  B,  obviously  the 
left  eye  looking  through  A  will  see  any  object  at  the 
point  D  directly  in  front  of  the  opening.  The  right  eye, 
looking  through  J5,  will  not  receive  light  directly  from  the 
object  0 ,  but  will  receive  its  light  only  after  it  has  been  re- 
flected from  the  mirror  M'  into  the  mirror  M  and  then 
through  the  opening  B.  (For  convenience  in  drawing,  the 
rays  of  light  from  the  object  0  and  D  to  the  two  eyes  are 
represented  as  parallel,  that  is,  as  coming  from  a  very  re- 
mote object.)  The  effect  of  this  double  reflection  is  to  throw 
into  the  right  eye  the  image  that  would  be  received  by  the 
eye  placed  in  the  position  of  the  mirror  marked  M'.  The 
right  eye,  therefore,  gets  its  image  from  a  position  at  the 
left  of  the  left  eye  and  the  relation  between  the  two  eyes  is 
thus  reversed;  for  the  right  eye  gets  its  image  from  what 
is  relatively  the  left-hand  side  of  the  object,  and  the  left 


92    LABORATORY  EQUIPMENT  FOR 

eye  gets  its  image  from  what  is  relatively  the  right-hand 
side  of  the  object.  The  result  of  such  an  interchange  of 
the  images  in  the  two  eyes  will  be  that  solid  objects  will 
appear  hollow  and  more  remote  objects  will  appear  near 
at  hand.  It  will  be  very  difficult  for  the  observer  trained 
in  the  ordinary  observation  of  solid  objects  to  get  the  in- 
terpretation of  the  hollowness  from  familiar  objects.  It 
will  be  easier  to  get  the  interpretation  of  changes  in  rela- 
tive position,  near  objects  appearing  far  away  and  remote 
objects  near.  The  observation  can  be  facilitated  by  using 
objects  which  are  very  little  shaded,  and  by  asking  the  ob- 
server to  wink  his  eyes  during  the  observation.  This 
winking  of  the  eyes  makes  the  adjustment  between  the 
two  eyes  relatively  easier. 

The  pseudoscope  described  thus  far  may  be  transformed 
into  a  telestereoscope  by  using  the  two  openings  B  and  L 
instead  of  the  openings  A  and  B.  The  right  eye,  which  in 
this  case  is  looking  through  the  opening  B,  will  get  its 
image  not  from  directly  in  front,  but  from  the  position 
M'.  The  distance  between  the  two  eyes  will  then  be  ex- 
aggerated by  the  double  reflection  through  the  mirrors, 
and  the  object  will  be  seen  under  a  greater  parallax  than 
when  the  two  eyes  are  observing  it  in  their  ordinary  posi- 
tions. 

There  are  a  variety  of  forms  of  stereoscopes  and  pseudo- 
scopes  ;  perhaps  the  best  known  of  the  former  is  the  lens  stere- 
oscope popularly  known  as  a  toy.  The  lens  stereoscope  is 
somewhat  more  complex  in  principle  than  the  mirror  stereo- 
scope and  for  this  reason  is  not  as  good  for  laboratory 
work.  It  can  be  used,  however,  and  figures  on  a  reduced 
scale  can  be  prepared  as  required  in  the  exercise.  The 
lenses  in  such  a  stereoscope  serve  two  distinct  functions. 
From  their  shape  and  position  they  act  first  as  prisms 
and  deflect  the  rays.  Secondly,  in  their  capacity  as  lenses 


PSYCHOLOGICAL  EXPERIMENTS 


93 


they  assist  the  eye  to  focus  the  light  from  the  figures.  In 
order  to  make  clear  these  two  functions,  Fig.  42  shows  in 
full  drawn  lines  two  prisms  in  the  positions  occupied  in 
the  ordinary  lens  stereoscope  by  the  lenses.  It  will  be 


noticed  that  the  two  faces  of  the  prisms  turned  towards 
the  two  eyes  are  in  the  same  plane.  The  surfaces  of  the 
prism  more  remote  from  the  eyes  are  oblique.  Rays 
of  light  from  A  and  5,  which  represent  the  figures,  will  be 
deflected  in  passing  through  the  prisms,  as  indicated  in 


94          LABORATORY  EQUIPMENT  FOR 

XXF  and  YYF'.  The  two  eyes  receiving  the  rays  XX F 
and  YYF' will  be  converged, and  the  observer  will  interpret 
the  two  rays  as  if  they  came  from  the  single  point  R  be- 
hind the  true  figures.  If  the  figures  A  and  B  are  of  suit- 
able character  they  will  fuse  and  the  observer  will  see  a 
single  solid  object  at  R.  Obviously  a  conflict  similar  to 
that  described  in  the  case  of  the  mirror  stereoscope  will 
arise  between  the  reflex  tendency  of  the  lens  of  the  eyes  to 
focus  upon  R  and  the  requirement  that  they  focus  the  light 
from  A  and  B.  In  this  stereoscope 
the  conflict  is  not  overcome  by  the 
effort  of  the  observer,  but  by  plac- 
ing lenses  in  the  position  of  the 
prisms.  The  lenses  are  placed  in 
the  position  indicated  by  dotted  lines 
in  Fig.  42.  Here  they  serve  all  the 
purposes  of  deflecting  prisms  and, 
furthermore,  aid  the  lenses  of  the 
eyes  in  focusing  the  light  from  A 
and  B,  which  light  comes  from  a  po- 
sition nearer  than  R,  upon  which  the 
eyes  are  converged  and  for  which 
the  lenses  are  naturally  focused. 

A  great  variety  of  figures  suitable 
for  use  with  the  lens  stereoscope  can 
be  purchased  of  any  one  of  the 
stereoscope  supply  companies.  Underwood  &  Under- 
wood of  New  York  City,  19th  Street  and  Fifth  Avenue, 
have  a  collection  of  sterograms  which  cover  most  of  the 
important  phenomena  of  binocular  vision. 

Another  form  of  stereoscope  is  illustrated  in  Fig.  43. 
With  some  training  an  observer  may  accustom  himself 
to  the  fusion  of  figures  of  the  kind  usually  used  in  stereo- 
scopes without  the  aid  of  any  apparatus  whatsoever.     If, 


Km. 


PSYCHOLOGICAL  EXPERIMENTS          95 

for  example,  the  image  appropriate  to  the  right  eye  is 
drawn  on  a  card  and  the  image  for  the  left  eye  is  drawn  on 
a  second  card,  and  these  two  cards  are  placed  in  the  posi- 
tions A  and  B,  Fig.  44,  A,  and  the  two  eyes  are  voluntarily 
crossed  so  that  the  axes  of  vision  are  along  the  lines  AF 
and  BFf,  there  will  be  seen  at  0  a  single  solid  object 
which  results  from  the  fusion  of  the  two  images  derived 
from  A  and  B.  If  the  two  cards  A  and  B  are  appropriate 
in  form  and  nearer  than  the  two  eyes,  fusion  may  take 
place  as  indicated  in  Fig.  44,  B.  The  fused  image  will 


FIG.  44 


in  this  case  appear  at  R.  Such  fusion  requires  practice 
in  order  to  dissociate  convergence  and  accommodation, 
for  obviously  in  both  cases  the  lenses  of  the  eyes  must  focus 
light  coming  from  a  point  other  than  the  point  of  fixation. 
The  whole  matter  of  retinal  rivalry  is  a  fruitful  field  for 
investigation.  There  are  undoubtedly  great  individual 
differences  in  observers  in  the  ability  to  fuse  different 
colors,  and  the  strain  which  is  produced  by  the  effort  to 
fixate  two  objects  undoubtedly  influences  the  rate  of  rivalry. 
Dr.  Breese  in  his  paper  "  On  Inhibition,"  Monograph  Sup- 


96          LABORATORY  EQUIPMENT  FOR 

plement  of  the  Psychological  Review,  No.  11,  reports  a 
number  of  experiments  on  retinal  rivalry  in  which  he  has 
shown  that  the  movements  of  the  eyes  are  important  ele- 
ments in  determining  the  degree  of  fusion  of  two  rival 
fields.  There  is  one  special  case  of  partial  fusion  which 
properly  belongs  under  the  general  head  of  retinal  rivalry. 
If  two  fields  which  are  otherwise  suitable  for  fusion  are 
different  from  each  other  in  that  one  is  black  and  the  other 
white,  there  will  be  a  unique  type  of  fusion  resulting  in 
metallic  luster.  This  metallic  luster  corresponds  di- 
rectly to  what  is  seen  in  ordinary  experience  under  similar 
conditions.  If  one  looks,  for  example,  at  a  metallic  sur- 
face which  is  illuminated  from  some  definite  source  of 
light,  this  surface  will  reflect  more  light  into  one  eye  than 
into  the  other.  This  is  equivalent  to  saying  that  one 
surface  is  dark  while  the  other  is  relatively  light.  The 
observer  who  looks  with  two  eyes  at  such  a  surface  will 
not  only  see  the  surface  but  will  also  see  the  luster,  which 
is  shown  by  the  stereoscopic  experiment  to  be  due  to  the 
inequality  in  the  illuminations  of  the  surfaces.  If  now 
the  coloring  of  the  surfaces  differs  not  only  in  intensity 
but  also  in  quality,  the  fusion  becomes  still  more  incom- 
plete with  the  results  noted  in  rivalry. 

Methods  of  recording  the  rate  of  rivalry  will  be  described 
in  connection  with  Exercise  XXII.  These  methods  in- 
volve certain  recording  apparatus  which  will  be  in  constant 
use  in  the  second  part  of  the  course,  but  is  not  needed  in 
general  in  this  part. 

The  exact  point  upon  which  the  two  eyes  are  converged 
when  two  images  are  fused  by  means  of  a  stereoscope  is 
impossible  to  define  from  direct  introspection.  It  can  be 
determined  by  finding  out  the  positions  of  the  lines  of  re- 
gard. The  method  of  procedure,  if  one  is  using  a  mirror 
stereoscope,  is  to  find  on  the  two  mirrors  the  points  from 


PSYCHOLOGICAL  EXPERIMENTS          97 

which  the  rays  enter  the  two  eyes  from  what  seems  to  be 
in  the  fused  image  a  single  point.  This  can  be  done  by 
moving  a  lead  pencil  successively  across  the  two  mirrors 
until  its  point  seems  to  coincide  with  the  point  chosen. 
The  distance  between  the  two  points  on  the  two  mirrors 
should  now  be  measured;  the  distance  between  the  two 
eyes  should  be  measured,  and  the  distance  between  the 
eyes  and  the  mirrors.  If  the  distance  between  the  two 
eyes  is  regarded  as  the  base  of  a  triangle  at  whose  ver- 
tex the  point  of  fixation  lies,  the  distance  of  this  point 
of  fixation  can  readily  be  plotted  by  recognizing  that  the 
distance  between  the  two  points  on  the  mirrors  is  the  base 
of  a  second  similar  triangle  which  also  has  as  its  vertex  the 
point  of  fixation.  The  distance  between  the  two  bases 
of  the  two  similar  triangles  is  the  known  distance  between 
the  eyes  and  the  mirrors.  The  whole  matter  can  be  plotted 
as  shown  in  Fig.  38  (page  83).  When  the  lens  stereo- 
scope is  used  instead  of  the  mirror  stereoscope,  it  is  some- 
what more  difficult  to  determine  the  point  of  fixation,  be- 
cause the  lenses  are  so  near  to  the  eyes.  In  this  case  some 
object  should  be  interposed  between  the  lens  of  the  stereo- 
scope and  the  eye.  The  two  points  on  the  surfaces  of  the 
lenses  near  the  eyes  can  now  be  ascertained  which  cor- 
respond to  a  single  fused  part  of  the  object.  Further 
procedure  is  similar  to  that  followed  in  the  case  of  the 
mirror  stereoscope. 


EXERCISE  VI 

A — APPARATUS   AND   PROCEDURE 

The  head  must  be  held  in  a  fixed  position  in  this  experi- 
ment. To  this  end  the  head-rest  described  on  page  32 
may  be  used,  or  rods  may  be  clamped  to  the  chair  in  which 
the  observer  sits.  In  either  case  the  space  back  of  the 
head  and  around  the  ears  must  be  left  free. 

Any  means  of  producing  an  easily  controlled  sound  of 
small  intensity  will  serve  the  purpose  of  this  exercise, 
though  telephones  are  so  much  better  than  any  other  form 
of  sounder  that  they  are  explicitly  referred  to  in  the  text. 
There  is  a  child's  toy  known  as  a  snapper,  or  sometimes 
called  a  telegraph  sounder,  which  is  very  convenient.  This 
toy  can  be  made  to  produce  a  sharp  single  click  by  pressing 
upon  a  spring.  The  noise  produced  by  this  snapper  is 
especially  advantageous  for  this  experiment,  because  it  is 
simple  in  quality  and  is  very  little  modified  by  the  position 
of  the  snapper  in  front  of  the  ear  or  behind  it. 

The  greater  convenience  of  telephones  as  sources  of  the 
sounds  consists  in  the  fact  that  telephones  can  be  easily 
controlled  in  their  positions  and  the  sound  can  be  pro- 
duced in  two  or  more  telephones  at  exactly  the  same  in- 
stant. In  the  parts  of  the  experiment  which  require 
more  than  one  sound  at  the  same  time,  the  use  of  two 
snappers  is  difficult,  because  the  experimenter  must  de- 
pend upon  his  own  ability  to  produce  the  sounds  at  ex- 
actly the  same  instant.  Two  or  more  telephones  can  be 
utilized  by  passing  the  same  electric  current  through  them. 
When  this  electric  current  is  made  or  broken  both  tele- 


PSYCHOLOGICAL  EXPERIMENTS 


99 


phones  will  act  in  exact  harmony.  The  watch  case  tele- 
phones, so  called,  are  better  than  the  larger  receivers  for 
the  purposes  of  this  experiment,  They  are  smaller  and 
can  therefore  be  better  held  in  position.  As  many  of 
these  telephones  as  are  necessary  for  the  experiment 
should  be  put  in  circuit  with  one  of  the  batteries  referred 
to  in  the  general  introduction  as  yielding  about  one  am- 
pere of  current.  In  the  circuit  should  also  be  placed  a 
mercury  switch;  this  can  be  used  in  making  and  breaking  the 
circuit  and  does  not  interfere  with  the  experiment  by  itself 
producing  a  click. 
The  simple  method 
of  using  the  make- 
and-break  current 
to  sound  the  tele- 
phones has  one  dis- 
advantage. Unless 
the  telephones  are 
tuned  exactly  to  the 
same  pitch,  it  is 
sometimes  possible 
to  distinguish  them 
because  of  their 
difference  in  quality.  This  difficulty  can  be  overcome  by 
putting  into  the  circuit  a  simple  interrupter.  When  the 
interrupted  current  is  allowed  to  pass  through  the  tele- 
phones, the  result  will  be  a  series  of  vibrations  of  the 
telephone  diaphragm  rather  than  a  single  click.  Minute 
differences  in  the  pitch  of  the  telephone  diaphragm  will 
then  be  entirely  overcome,  and  the  sound  will  be  somewhat 
clearer  and  easier  to  locate  than  with  the  single  clicks. 
The  principle  of  the  interrupter  is  one  which  is  used 
in  a  great  many  pieces  of  apparatus  employed  in  the  labor- 
atory, and  it  may  be  described  at  this  point  in  some  de- 


Fio.  45 
From  the  catalogue  of  C.  H.  Stoelling  Co.,  Chicago 


100        LABORATORY  EQUIPMENT  FOR 

tail.  The  rod  A,  Fig.  45,  is  held  firmly  in  position  by  the 
heavy  post  shown  at  the  left  of  the  figure.  The  rod  car- 
ries at  its  right  end  a  long  platinum  needle  which  extends 
downward  into  a  mercury  cup.  From  the  mercury  cup  a 
wire  extends  to  the  electromagnet  which  is  held  above 
the  rod  A.  The  electromagnet  is  insulated  from  the  rest 
of  the  apparatus  and  is  connected  at  the  end  of  its  coil 
opposite  to  that  at  which  it  is  connected  with  the  mer- 
cury cup,  with  the  battery.  The  other  pole  of  the  battery 
is  connected  with  the  rod  A  through  the  metallic  post.  As 
soon  as  the  platinum  needle  is  pushed  downward  so  as 
to  dip  into  the  mercury  cup  a  complete  electric  circuit  is 
made  which  passes  through  the  magnet.  As  soon  as  the 
magnet  becomes  active  it  pulls  the  rod  A  upward  and 
thus  tends  to  draw  the  platinum  needle  out  of  the  mercury 
cup  and  to  break  the  circuit.  As  soon  as  this  is  done 
the  magnet  is  no  longer  active,  and  the  rod  A  by  its  own 
elasticity  oscillates  back  again  so  as  to  make  a  contact 
between  the  mercury  cup  and  the  platinum  needle.  This 
renews  the  electric  current,  causes  the  magnet  to  pull  the 
bar  A  up  again,  breaks  the  circuit,  and  the  whole  opera- 
tion is  again  repeated.  The  rate  at  which  the  electric 
current  will  be  interrupted  depends  upon  the  rate  at 
which  the  rod  A  oscillates.  In  some  other  forms  of  inter- 
rupters the  contact  here  provided  by  the  mercury  cup 
and  platinum  needle  is  made  by  means  of  an  elastic 
platinum  wire  and  a  fixed  metallic  plate.  The  use  of 
platinum  in  all  of  these  contrivances  is  necessary  because 
there  is  an  electric  spark  each  time  the  current  is  broken, 
and  this  spark  would  very  soon  burn  any  other  metal. 
Furthermore,  in  the  mercury  contact  it  is  desirable  that 
the  mercury  surface  be  covered  by  a  drop  of  alcohol  or 
water  which  will  take  up  the  fumes  from  the  burning 
mercury. 


PSYCHOLOGICAL  EXPERIMENT^/    *'M- 

Contrivances  for  holding  the  telephones  in  position 
may  be  made  as  elaborate  as  desired.  The  most  conven- 
ient method  of  fastening  the  telephones  and  measuring 
their  positions  is  to  prepare  an  auditory  cage.  In  its 
simplest  form  this  cage  may  be  made  of  wooden  hoops. 
A  somewhat  more  elaborate  form  of  auditory  cage  is  rep- 
resented in  Fig.  46.  The  simpler  form  made  of  wooden 
hoops  is  constructed  on  the  same  principle  and  will  be 


FIG.  46 

readily  understood  from  the  following  description  of  the 
more  elaborate  form.  A  circular  metallic  ring  AAA  is 
supported  by  similar  metallic  semicircles  CC  and  DD. 
These  semicircles  cross  each  other  and  are  fastened  firmly 
at  a  point  M  just  over  the  middle  of  the  circle  AAA. 
From  this  point  M  a  bar  is  carried  upward,  as  shown  at 
EE.  This  can  be  held  at  any  point  that  may  be  convenient. 
In  the  figure,  EE  passes  through  the  tube  F  which  is 
held  in  the  bracket  BB.  EE  is  held  in  position  by  the 


192         LABORATORY  EQUIPMENT  FOR 

collar  G  which  is  clamped  to  it  by  means  of  a  set  screw 
H .  If  the  collar  G  is  loosened  the  shaft  EE  may  be  ad- 
justed so  as  to  bring  the  cage  to  a  higher  or  lower  point  to 
suit  a  given  observer.  The  whole  cage  may  be  rotated 
within  the  carrier  F,  so  that  any  point  on  the  circle  AAA 
may  be  brought  into  any  desired  horizontal  position.  A 
circular  disk  R  is  clamped  on  the  outside  of  the  carrier 
F  by  means  of  a  screw.  This  disk  has  graduations  marked 
upon  it  to  indicate  degrees,  and  a  pointer  is  brought  up 
from  the  shaft  EE,  as  indicated  at  L,  so  that  the  position 
of  the  pointer  and  therefore  of  the  whole  cage  can  be  read 
on  the  circular  disk  R. 

The  telephones  are  now  fastened  on  the  frame  AAAt 
or  on  the  side  pieces  C  or  D,  and  the  cage 
can  be  rotated  as  the  experimenter  desires. 
A  convenient  method  of  fastening  the 
telephones  to  the  frame  is  represented  in 
Fig.  47.  C  represents  a  section  of  the 
frame.  The  bent  metal  plate  A  hooks  over 
the  top  of  the  frame.  Below  there  is  a 
screw  /S,  which  controls  an  adjustable  tooth 
H.  When  H  is  screwed  against  A,  the  whole  is  firmly 
clamped  to  C.  When,  on  the  other  hand,  S  is  loosened, 
H  falls  down  and  permits  A  to  be  carried  to  any  part  of 
the  frame  desired.  A  is  riveted  to  the  back  of  a  telephone 
which  is  by  this  means  easily  clamped  to  any  part  of  the 
cage. 

A  simpler  form  of  holder  can  be  devised  by  using  a  piece 
of  spring  brass  which  can  be  bent  into  a  clip  and  slipped 
over  the  frame. 

Another  attachment  necessary  for  the  first  part  of  the 
experiment  is  a  rod  which  can  be  fastened  to  the  cage  in  a 
horizontal  position.  Along  this  rod  slides  a  carriage  to 
which  a  telephone  may  be  clamped. 


PSYCHOLOGICAL  EXPERIMENTS         103 

The  various  parts  of  the  frame  of  the  cage  should  be 
graduated  in  degrees  and  the  rod  should  be  graduated  in 
centimeters. 

The  whole  cage  can  be  supported  in  various  ways.  It 
is  desirable  to  support  it  at  a  distance  from  any  large 
surface  which  could  serve  to  give  an  echo  of  the  sounds. 
The  best  device  for  supporting  any  cage  is  a  high  stand 
made  of  a  heavy  base  and  a  piece  of  iron  pipe,  such  as 
is  used  for  steam  or  water  connections.  For  ordinary 
purposes  of  class  work,  it  is  possible  to  fasten  the  cage 
to  a  bracket  extending  from  a  wall  of  the  room.  The 
experiment  will  be  somewhat  interfered  with  by  the  echo 
from  the  wall,  but  if  the  sounds  are  not  too  intense  the  dis- 
advantages of  this  method  will  be  reduced  to  a  minimum. 

Any  form  of  cage  which  offers  large  reflecting  surfaces 
of  wood  or  metal  is  objectionable;  the  metal  strips  used  for 
the  cage  should,  therefore,  be  as  narrow  as  practicable. 
The  fact  that  the  experimenter  must  stand  near  the  cage 
is  also  an  objection  to  the  device  thus  far  described. 
This  difficulty  can  be  overcome  by  more  elaborate  devices 
for  adjusting  the  cage  by  means  of  strings  carried  to  a  dis- 
tance from  the  cage. 

A  very  elaborate  auditory  cage  is  described  by  Professor 
Seashore  in  the  Psychological  Review,  Vol.  X,  pp.  64-68, 
and  in  Monograph  Supplement  of  the  Psychological  Re- 
view, No.  28,  pp.  1-5. 

B — RESULTS 

The  following  series  of  observations  was  reported  for 
the  first  part  of  the  experiment,  when  one  telephone  was 
kept  in  a  fixed  position  50  cm.  from  the  left  ear  in  the 
same  horizontal  plane  as  the  ear  and  in  a  line  pass- 
ing through  the  two  ears,  and  the  other  telephone 


104        LABORATORY  EQUIPMENT  FOR 

was  moved  in  the  same  line  through  various  distances 
from  the  right  ear. 


Distance    of 

second  tele- 

phone from 

Apparent  position 

Apparent  distance  from  head 

right  ear  in 

cms. 

10 

Right,  about  5°  to  rear 

Near  head,  10  cm.  distant 

20 

Right,  about  20°  to  rear 

Further  away,  perhaps 

20cm. 

30 

Right,  about  50°  to  rear 

Still  further,  30-40  cm. 

40 

Rear,  about  10°  to  right 

Still  further,  40-50  cm. 

50 

Rear,  perhaps  5°  to  right 

Still  further,  50  cm. 

60 

Rear,  about  10°  to  left 

50  cm.  distant 

70 

Rear,  about  25°  to  left 

Same  as  last 

80 

Left,  about  45°  to  rear 

Same  as  last 

90 

Left,  about  30°  to  rear 

Same  as  last 

100 

Left,  about  20°  to  rear 

Same  as  last 

In  the  second  part  of  the  exercise  the  distances  through 
which  the  telephones  must  be  moved  were  found  by  vari- 
ous observers  as  follows : 


Starting  in  median  plane  in 
front  or  behind  and  moving 
to  right  or  left 

Starting   opposite  one  ear  and 
moving     forward     or     back- 
ward 

Observer 

Avg. 

M.V. 

M.V. 

A 
B 
C 
D 

3° 

5° 
6° 

8° 

0.4 
0.3 
0.7 
0.6 

Avg.  25° 
15°-20° 
30°-40° 
Avg.  40° 

4.3  * 
6.0 

C — SUPPLEMENTARY   EXPERIMENTS 

If  complex  tones  are  used  it  will  be  found  that  there  is 
much  more  complete  discrimination  of  positions  in  front 


PSYCHOLOGICAL  EXPERIMENTS         105 

of  the  head  and  behind.  This  is  probably  due  to  the  fact 
that  the  pinna  in  reflecting  the  sound  into  the  ears  modi- 
fies the  sound  somewhat  by  reinforcing  certain  of  its 
components.  This  action  of  the  pinna  as  a  resonator  is 
different  according  to  the  direction  from  which  the  sound 
comes.  , 

The  second  supplementary  experiment  which  uses  tun- 
ing-forks in  direct  contact  with  the  head  is  of  some  interest 
because  the  bones  of  the  skull  transmit  the  sounds  directly 
to  the  two  inner  ears.  The  apparent  localization  of  the 
fused  resultant  is  often  inside  of  the  skull. 

Oblique  positions  give  complications  of  the  results  re- 
ported for  horizontal  positions.  Variations  in  the  qual- 
ity of  components  have  been  reported  as  giving  variations 
in  the  vertical  or  oblique  positions  of  the  fused  resultant. 
Variations  in  the  pitch  can  be  produced  by  using  dia- 
phragms of  different  thicknesses  in  the  telephones,  or  by 
loading  an  ordinary  diaphragm  with  lead.  If  the  differ- 
ence between  the  two  sounds  is  too  great  they  will  not  fuse. 

If  reflectors  are  fastened  to  the  ears  the  effect  of  the 
pinnas  as  resonators  is  entirely  changed,  and  as  a  result 
the  apparent  location  of  the  sound  will  be  modified. 

Improvement  of  auditory  localization  through  practice 
is  reported  by  Pierce  in  his  "Studies  in  Auditory  and 
Visual  Perception." 

The  use  of  three  telephones  complicates  the  problem 
by  introducing  one  factor  which  may  dominate  the  whole 
experience  (if,  for  example,  one  source  of  sound  is  out- 
side of  the  median  plane  and  the  other  two  are  in  that 
plane).  This  is  a  case  which  differs  radically  from  color 
and  light  fusions. 


EXERCISE  VII 

A — APPARATUS    AND    PROCEDURE 

The  simplest  method  of  producing  tones  for  the  pur- 
poses of  this  exercise  is  by  means  of  a  set  of  Quincke 
tubes.  A  Quincke  tube  is  represented  in  Fig.  48.  It 
consists  essentially  of  a  blower  B  held  by  means  of  a  wire 
in  front  of  a  sounder  *S.  The  sounder  is  stopped  at  one 
extremity  by  means  of  a  cork.  If  the  blower  is  held  in  the 
right  position  at  the  mouth  of  the  tube,  a  fairly  pure  note 
may  be  produced  by  blowing  through  B. 
The  air  for  the  blower  can  be  supplied 
most  readily  by  the  mouth.  If  it  is  de- 
sired to  blow  more  than  one  tube  at  a 
time,  as  in  the  experiment,  a  mouthpiece 
can  be  made  from  tin  with  a  single  open- 
ing at  one  end  to  be  inserted  in  the  mouth, 
and  two  or  more  openings  of  appropriate 
size  to  fit  over  the  blowers  of  the  de- 
sired number  of  tubes  at  the  other  end. 
Quincke's  tubes  can  be  made  to  produce 
FlG  48  tones  of  relatively  high  pitch. 

A  second  simple  means  of  producing  musical  tones  of 
desired  pitch  is  to  employ  two  or  more  chromatic  pitch- 
pipes.  The  form  of  pipe  diagrammatically  represented 
in  Fig.  49  serves  the  purpose  very  well.  The  reed  pipe 
PP  is  supplied  with  a  sliding  damper  DD.  The  foot  of 
the  damper  rests  on  the  reed  RR  and  may  be  drawn  up 
or  down  so  as  to  make  the  reed  longer  or  shorter,  and  the 
note  of  the  pipe  consequently  lower  or  higher.  If  a  scale 

106 


PSYCHOLOGICAL  EXPERIMENTS         107 

is  attached  to  the  damper  at  some  point,  any  desired 
note  may  be  produced  and  read  on  the  scale.  Two  such 
pipes  with  a  combination  mouthpiece,  such  as  that  de- 


FIG.  49 


scribed  in  connection  with  the  discussion  of  the  Quincke 
tubes,  will  serve  very  well  the  purposes  of  the  exercise. 

Even  with  the  simple  devices  thus  far  described,  it  is 
desirable  to  provide  an  air  supply  which  shall  be  more 
constant  in  intensity  than  that  which  can  be  produced  by 


FIQ.  50 


blowing  with  the  mouth.  A  simple  type  of  air  reservoir 
consists  of  a  large  vessel  indicated  in  Fig.  50.  This  outer 
vessel  A  should  be  two-thirds  filled  with  water.  A  second 


108        LABORATORY  EQUIPMENT  FOR 

vessel  of  like  form  should  be  inverted  in  the  position  By 
and  tubes  D  and  E  should  be  introduced  through  the  outer 
vessel  and  led  upward  into  B  above  the  level  of  the  water. 
Air  may  be  introduced  into  the  vessel  B  through  the  tube 
D  from  any  convenient  source.  A  hand  or  foot  bellows, 
a  foot  pump,  or  a  mechanical  pump,  may  be  used  to  sup- 
ply air  for  this  purpose.  When  the  air  is  needed  to  blow 
the  pipes  it  should  be  drawn  from  the  second  tube  E. 
The  reservoir  B  will  act  as  a  storage  reservoir  and 
through  its  weight  it  will  also  tend  to  force  the  air  out 
under  a  constant  pressure.  The  pressure  can  be  increased 
by  placing  on  top  of  the  reservoir  various  weights. 

If  it  is  desired  to  use  a  current  of  air  for  any  lengthy 
experiments,  automatic  mechanical  contrivances  can  be 
introduced  into  the  supply  pipe  Z),  so  as  to  open  or 
close  the  supply  pipe  and  start  the  pump  according  to  the 
height  of  the  reservoir  B.  A  stop-cock  at  H  should  open 
when  the  reservoir  B  approaches  its  lower  limit  and  a  con- 
nection from  K  should  start  the  pump.  The  air  will  then 
be  allowed  to  enter  and  raise  the  tank  B.  The  stop-cock 
should  be  gradually  closed  during  this  raising  of  the  tank 
B,  until  finally  the  reservoir  is  completely  filled  ready  for 
the  experiment,  at  which  time  the  pump  may  be  stopped. 

Titchener  and  Whipple  describe  a  double  reservoir 
(American  Journal  of  Psychology,  1903,  pp.  107-1 1 2).  Two 
tanks  corresponding  to  B  in  the  figure  are  chained  to- 
gether so  that  one  rises  as  the  other  falls.  The  falling 
tank  is  provided  with  weights.  By  transferring  the 
weights  from  one  movable  tank  to  the  other,  a  stream  of 
air  under  very  uniform  pressure  can  be  supplied  with 
no  interruption  except  that  involved  in  transferring  the 
weights. 

A  mechanical  pump  can  be  used  with  a  storage  reser- 
voir without  the  pressure  tank  here  described.  In  that 


PSYCHOLOGICAL  EXPERIMENTS         109 

case,  since  the  air  is  delivered  from  the  storage  reservoir 
at  an  irregular  pressure,  a  double  regulator  valve  should 
be  secured  which  will  so  regulate  the  outflow  that  the  air 
can  be  delivered  at  the  point  of  use  at  a  uniform  low 
pressure.  Such  valves  are  to  be  had  through  any  mechanics' 
supply  house.  They  are  manufactured  by  Wm.  Boekel 
&  Co.,  518  Vine  St.,  Philadelphia.  (Catalogue  E.) 

Even  when  blown  steadily  by  means  of  an  automatic 
air-pump,  Quincke's  tubes  and  chromatic  pitch-pipes  are 


Fio.  51 

less  constant  in  their  qualities  than  organ  pipes.  A  sys- 
tem of  organ  pipes  mounted  on  a  keyboard  will  be  found 
to  be  a  very  satisfactory  means  of  supplying  tones.  The 
practical  difficulty  in  securing  this  kind  of  equipment 
consists  usually  in  getting  the  keyboard  for  sounding  the 
pipes  rather  than  in  securing  sets  of  pipes.  Fig.  51  shows 
the  mechanism  of  a  keyboard,  such  as  is  commonly  used 
in  pipe  organs.  The  air  chest  AA  has  two  openings,  one 
very  small  one  at  C,  and  a  large  one  at  K.  The  one  at  C 
is  always  open  and  tends  to  keep  the  air  in  the  small 


110        LABORATORY  EQUIPMENT  FOR 

outer  chamber  B  with  which  it  communicates  at  the  same 
pressure  as  the  air  inside  the  air  chest  A  A.  The  open- 
ing K  is  closed  by  the  valve  KJ.  This  valve  consists  of 
an  arm  J  with  a  fulcrum  at  its  center.  At  the  end  K  is  a 
felt  foot  fitting  over  the  opening  which  leads  out  of  the  air 
chest.  At  the  opposite  end  the  arm  J  is  fastened  to  a  piece 
of  flexible  sheepskin  M.  The  valve  K J,  is  held  in  position 


Fio.  52 
From  the  catalogue  of  Kohl,  Chemnitz,  Germany 

by  the  pressure  of  air  within  the  air  chest  and  by  the  small 
supplementary  spring  L.  The  valve  K  J  is  opened  indi- 
rectly by  reducing  the  pressure  on  the  outside  of  the  sheep- 
skin M.  This  is  accomplished  by  opening  the  valve  D 
which  communicates  with  the  outer  air.  The  valve  at  D 
can  be  opened  by  pressing  on  the  finger  piece  E.  As  soon 
as  the  pressure  in  B  is  reduced,  the  sheepskin  M  is  forced 


PSYCHOLOGICAL  EXPERIMENTS         111 

outward  and  opens  the  valve  K.  This  allows  the  air  to 
pass  out  of  the  air  chest  AA  into  the  organ  pipe  P. 

Elaborate  instruments  for  producing  series  of  tones  are 
manufactured.  Appunn's  "tone  messer"  is  a  reed  pipe 
in  which  the  successive  pipes  differ  from  each  other,  not 
by  the  conventional  intervals,  but  by  two  vibrations  in 
each  case. 

Stern  has  worked  out  an  apparatus  called  a  "tone-vari- 
ator"  for  producing  continuous  series  of  variations  in 
tonal  quality.  This  is  represented  in  Fig.  52.  The  me- 
tallic cylinder  C  has  a  piston  Kb  which  is  raised  and  low- 
ered from  below  by  a  cam.  The  volume  of  air  within 


FIG.  53 
From  the  catalogue  of  C.  H.  Stoelting  Co.,  Chicago 

the  cylinder  is  thus  varied  by  any  desired  amount,  and 
the  change  can  be  read  directly  on  the  scale  connected 
with  the  cam.  A  pipe,  A,  which  extends  obliquely 
down  to  the  mouth  of  the  cylinder,  excites  the 
cylinder  whenever  an  air  current  passes  through  it.  This 
apparatus  has  the  advantage  of  producing  not  merely  a 
variety  of  tones,  but  every  possible  modification  of  pitch. 
The  range  of  a  single  cylinder  is  limited  and  a  series  of 
cylinders  must  be  provided  for  any  extended  experiments. 
Instead  of  wind  instruments  such  as  have  been  described 
up  to  this  point,  string  instruments  may  be  used.  The 
most  available  instrument  of  this  sort  is  the  sonometer 
represented  in  Fig.  53.  Over  a  resonator  box  are  stretched 


112        LABORATORY  EQUIPMENT  FOR 

wires.  Under  these  wires  are  adjustable  bridges  which 
may  be  placed  in  various  positions  along  scales  marked 
on  the  resonator.  The  wires  are  kept  under  tension 
either  by  weights,  as  shown  in  the  figure,  or  by  means  of 
screws.  The  tones  from  the  wires  are  clear  and  of  long 
duration.  They  differ  in  timbre  according  to  the  point 
at  which  the  wires  are  plucked  or  bowed  when  excited. 

Another  means  of  producing  continuous  series  of  tones 
is  by  means  of  weighted  tuning-forks  such  as  are  shown 
in  Fig.  54.  Tuning-forks  give  very  much  more  reliable 
tones  than  any  other  type  of  apparatus,  and  the  tones  are 
simpler  in  quality  than  any  that  can  be  secured  either 


FIG.  54 

After  Wundt.  "  Grundauge  der  physiologischen  Psychologic," 
5th  Ed.,  VoLII,  p.  82 

from  reeds,  organ  pipes,  or  string  instruments.  On  the 
other  hand,  the  tone  from  a  tuning-fork  is  by  no  means  as 
intense  as  the  tone  from  a  wind  instrument.  The  intensity 
of  the  tone  can  be  increased  by  mounting  the  forks  on 
resonating  boxes. 

The  simplicity  of  the  tones  from  tuning-forks  is  a  matter 
of  importance  for  the  complete  success  of  the  experiment 
with  the  fused  tones.  If  the  tones  are  at  all  complex, 
the  degree  of  fusion  will  depend  quite  as  much  upon  the 
other  components  as  upon  the  chief  or  fundamental  tone. 
For  this  reason  the  use  of  organ  pipes  or  stringed  instru- 
ments is  likely  to  result  in  a  discrimination  of  tones  even 


PSYCHOLOGICAL  EXPERIMENTS         113 

when  they  would  fuse  completely  if  they  were  simple. 
The  production  of  pure  tones  requires  the  very  best 
tuning-forks.  It  is  relatively  easy  to  produce  a  tuning- 
fork  which  shall  give  a  fairly  pure  tone,  but  if  the  mate- 
rial in  the  tuning-fork  is  irregular  in  its  temper  or  in  its 
density,  the  fork  will  vibrate  in  different  ways  in  its  dif- 
ferent parts  and  there  will  result  a  complex  tone.  For 
this  reason  the  best  quality  of  tuning-forks  will  be  found 
indispensable  for  reliable  scientific  work  with  tones. 
If  such  tuning-forks  are  secured,  the  second  problem 


FIG.  55 

From  Wundt's  "  Grundziige  der  physiologischen  Psychologic," 
5th  Ed.,  Vol.  II,  p.  82 

is  to  provide  for  the  transmission  of  the  sound  from  these 
forks  to  the  hearer.  It  is  not  a  satisfactory  method  to  ex- 
cite the  two  forks  successively  and  then  attempt  to  judge 
of  their  fusion,  for  the  successive  sounding  of  the  forks 
will  give  the  observer  opportunity  to  discriminate  the 
sounds  more  completely  than  he  could  if  the  sounds 
had  been  presented  to  him  together.  The  arrangement 
shown  in  Fig.  55  makes  it  possible  to  excite  the  forks 
without  giving  the  observer  an  opportunity  to  hear  them 
until  they  are  both  in  vigorous  action.  A  rubber  tube 


114        LABORATORY  EQUIPMENT  FOR 

(S  Z  0)  should  be  carried  through  a  heavy  wall  from  one 
room  into  the  next.  Indeed,  it  is  preferable  that  the 
tube  be  carried  through  a  still  greater  space.  In  any  case 
it  should  be  of  rubber  rather  than  of  rigid  material.  At 
the  end  O,  should  be  seated  the  observer  with  the  tube 
placed  against  the  ear.  For  this  purpose  a  glass  tube 
may  be  carried  from  the  rubber  to  the  ear  of  the  observer, 
this  glass  tube  being  shaped  so  as  to  fit  the  ear  of  the  ob- 
server. At  the  other  end  of  the  rubber  tube  there  may 
be,  in  addition  to  what  is  shown  in  the  figure,  a  stopcock 
by  means  of  which  the  tube  can  be  completely  closed  while 
the  experiment  is  in  preparation.  This  tube  should  be 
connected  with  two  or  more  resonators,  such  as  are  shown 
at  I,  II,  and  III.  A  very  convenient  method  of  procedure 
is  to  have  two  resonators,  one  of  which  is  fixed  in  size, 
the  other  of  which  has  a  piston  so  arranged  that  it  can  be 
adjusted  within  the  resonator,  reducing  it  to  the  proper 
size  for  any  one  of  the  forks  of  a  given  octave.  In  front  of 
the  resonators  should  be  clamped  the  forks  which  are  to 
be  used  in  the  experiment.  When  all  is  in  readiness  for 
the  experiment  the  observer  should  be  warned  that  he  is 
to  hear  the  sound  in  a  few  seconds.  The  tuning-forks 
should  be  excited  either  by  striking  them  or  by  bowing 
them  with  a  violin  bow.  The  shutters  in  front  of  the  reson- 
ators should  be  drawn  aside;  the  rubber  tube  should  be 
opened  so  as  to  transmit  the  sound  to  the  observer.  It 
may  be  found  necessary,  if  the  wall  between  the  observer 
and  the  apparatus  is  not  thick,  to  completely  disconnect 
the  rubber  tube  from  the  resonators  during  the  preparation 
for  the  experiment.  Furthermore,  in  order  to  prevent  the 
sound  from  being  transmitted  by  the  solid  walls,  it  is 
sometimes  necessary  to  suspend  the  resonators  and  the 
tuning-forks  from  springs  so  that  the  sound  may  be  pro- 
duced upon  an  isolated  bridge. 


PSYCHOLOGICAL  EXPERIMENTS         115 

The  intensity  of  the  tones  can  be  varied  by  exciting  the 
source  less  vigorously  or  by  cutting  off  part  of  the  conduct- 
ing channel  to  the  observer.  If  the  source  is  a  Quincke 
tube  or  reed-pipe  the  tube  which  carries  the  air  into  the 
tube  can  be  partly  closed.  The  effort  to  cut  down  the  in- 
tensity of  a  sound  after  it  has  been  produced  is  always 
complicated  by  the  fact  that  the  walls  of  the  conductor 
are  as  likely  to  carry  the  vibrations  as  the  columns  of  air 
inside  of  the  conductor.  It  is  better,  therefore,  to  regu- 
late the  sound  at  its  source. 

For  the  third  part  of  the  experiment  two  chromatic 
pitch-pipes  or  two  Stern's  variators  are  the  best  devices. 

In  working  with  intervals,  the  simplest  procedure  is  to 
have  one  source  adjustable  (for  example,  either  a  chro- 
matic pitch-pipe  or  a  tone-variator)  and  the  other  fixed. 
Now  sound  the  interval  between  the  two,  and  immediately 
after  vary  one  of  the  sources  slightly  and  repeat.  It  will 
be  found  that  the  ability  to  recognize  intervals  is  in  gen- 
eral very  highly  developed. 

B — RESULTS 

A  table  showing  the  distribution  of  judgments  in  the 
first  experiment  of  the  exercise  with  three  untrained  ob- 
servers is  as  follows: 

Judgments 


Combinations 

Certainly 
one  tone 

Probably 
one  tone 

Doubtful 

Probably 
two  tones 

Certainly 
one  tone 

cc 

3 

4 

3 

1 

1 

1 

1 

0 

0 

0 

0 

0 

0 

0 

1 

CB 

0 

0 

0 

0 

0 

0 

1 

0 

0 

1 

0 

0 

3 

5 

5 

CA 

1 

0 

1 

2 

0 

0 

0 

0 

1 

0 

2 

2 

2 

3 

1 

CG 

1 

1 

1 

3 

1 

2 

0 

1 

1 

1 

0 

1 

0 

2 

0 

CF 

1 

0 

0 

1 

0 

1 

2 

1 

3 

1 

2 

1 

0 

2 

0 

CE 

0 

1 

0 

0 

2 

1 

1 

0 

2 

3 

2 

1 

1 

0 

1 

CD 

0 

0 

1 

0 

0 

0 

0 

0 

0 

1 

0 

4 

4 

5 

0 

Observers 

A 

B 

c 

A 

B 

C 

A 

B 

C 

A 

B 

C 

A 

B 

C 

116  •      LABORATORY  EQUIPMENT  FOR 

The  degrees  of  fusion  here  indicated  do  not  agree  in  de- 
tail with  Stumpf's  table,  but  they  give  a  sufficiently  clear 
indication  of  the  difference  between  CC'  and  CG  on  the 
one  hand  and  such  combinations  as  CB  and  CD  on  the 
other  hand.  Stumpf  recognizes  five  degrees  of  fusion: 
from  the  most  complete  in  the  octave,  CC',  through  2d) 
the  fifth,  CG,  3d)  the  fourth,  CF,  4th)  the  pure  thirds 
and  sixths,  CE  and  CA,  to  5th)  minor  sevenths  and 
other  combinations,  CB  and  CD. 

When  one  tone  is  stronger  than  the  other,  fusion  is  more 
complete,  the  stronger  tone  dominating  the  whole  percept. 

The  ability  to  discriminate  tones  differs  greatly  with 
different  observers,  ranging  from  one  vibration  to  half  a 
tone.  If  will  be  found  in  some  cases  that  the  observer 
can  discriminate  tones  before  he  can  tell  which  is  higher. 

The  recognition  of  intervals,  as  pointed  out  above,  is 
often  better  than  the  recognition  of  tonal  differences. 

C — SUPPLEMENTARY   EXPERIMENTS 

The  apparatus  for  developing  combination  tones  is  the 
same  as  that  described.  Quincke  tubes  serve  very  well  for 
difference-tones,  adjustable  forks  for  beats.  For  pur- 
poses of  demonstrating  difference-tones  the  double  whistles 
which  are  supplied  as  bicycle  warning  whistles  sometimes 
give  a  very  marked  difference-tone. 

The  last  supplementary  experiment  which  deals  with 
highest  and  lowest  tones  requires  apparatus  not  described 
thus  far. 

Series  of  steel  cylinders  of  different  lengths  are  manu- 
factured which  make  it  possible  to  secure,  by  simply  strik- 
ing the  different  cylinders,  very  high  metallic  tones  which 
are  pure  in  quality  because  all  of  their  overtones  are  much 
beyond  the  range  of  ordinary  hearing. 


PSYCHOLOGICAL  EXPERIMENTS         117 

The  apparatus  most  convenient  for  securing  high  tones 
is  Galton's  whistle,  the  most  elaborate  form  of  which  is 
shown  in  Fig.  56.  This  whistle  consists  of  a  pair  of 
small  tubes,  D  and  E.  The  air  is  forced  into  D  and  so 
against  the  tip  of  E  from  the 
rubber  bulb.  Vibration  is  set 
up  in  E.  The  length  of  the  air 
column  in  E  is  regulated  by 
means  of  a  piston  controlled  by 
the  graduated  screw  G  and  F. 
The  rate  of  the  vibration  will  be 
determined  by  the  length  of  the 
air  column  in  E.  In  order  to 
prevent  transverse  vibrations,  the 
opening  between  D  and  E  is 
regulated  by  the  graduated  screw 
B.  There  is  a  simple  form  of 
this  whistle  which  is  subject  to 
certain  errors.  The  more  elab- 
orate form  supplied  by  Edelmann 
obviates  these  errors  and  gives  a  very  accurate  measure- 
ment of  the  highest  tones. 

For  the  lowest  audible  tones,  simple  rods  may  be  used. 
These  may  be  held  firmly  in  a  vise  and  shortened  or 
lengthened  until  the  limits  of  audibility  are  reached. 
A  simple  rod  made  for  this  purpose  is  supplied  by  Appunn. 


FIG.  56 

From  the  catalogue  of  Edel- 
mann, Munich,  Germany 


EXERCISE  VIII 


A — APPARATUS   AND   PROCEDURE 

Very  little  apparatus  is  required  for  Exercise  VIII. 
A  convenient  method  of  marking  the  arm  at  the  outset  of 
the  experiment  is  to  provide  a  rubber  stamp,  or,  better,  an 
electrotype  stamp,  which  has  on  its  face  a  figure  marked 
off  into  squares  two  millimeters  on  each  side.  Such  a 
stamp  as  this  can  be  used  with  the  ordinary  stamping 
pad  and  a  very  good  impression  can  be  produced  on  the 
skin.  An  impression  from  the  same  stamp  should  be 
repeated  in  the  notebook  of  the  experimenter  as  a  means 
of  making  a  record  of  the  differences  in 
sensitivity  discovered  during  the  explora- 
tion of  the  skin.  Fig.  57  shows  the  im- 
pression from  such  a  stamp. 

Points  for  the  exploration  of  the  skin 
can  be  provided  in  the  simplest  fashion 
by  beveling  the  end  of  a  short  brass 
rod  to  a  blunt  point.  The  point  should 
not  be  too  fine,  as  it  will  be  likely  to  prick  the  skin  and 
cause  discomfort  during  the  experiment.  On  the  other 
hand,  it  should  not  be  so  blunt  as  to  spread  the  stimulation 
diffusely  over  the  skin  so  as  to  affect  a  series  of  points  at 
the  same  time. 

In  order  that  the  hand  of  the  experimenter  may  not 
come  into  direct  contact  with  the  metal  rod  and  thus  serve 
as  a  means  of  rapidly  cooling  or  warming  it,  the  rod  should 
be  passed  through  a  cork  and  the  experimenter  should 
handle  the  rod  by  means  of  this  cork.  Such  a  metallic 

118 


Fig.  57 


PSYCHOLOGICAL  EXPERIMENTS         119 

point  as  this  may  be  placed  in  ice  water  if  it  is  desired  to 
experiment  with  cold  spots,  and  in  water  of  various  other 
degrees  of  temperature  if  it  is  desired  to  work  with  warm 
spots. 

More  convenient  forms  of  temperature  points  can  be 
made  as  indicated  in  Fig.  58.  The  handle  furnishes  a 
means  of  holding  the  point  which  may  be  renewed  as  often 
as  desired  from  a  supply  which  is  kept  in  cold  or  warm 
water. 

Instead  of  the  solid  points,  cylinders  may  be  used. 
These  can  be  filled  with  water  of  any  desired  temperature 
and  will  hold  their  temperature  longer  than  the  rods.  In 
the  most  elaborate  forms  of  temperature  cylinders,  a  cur- 
rent of  water  is  drawn  from  a  remote  reservoir,  where  it  is 
kept  at  the  desired  temperature, 

and  passed  continuously  through    *^  -V  *) 

the  cylinder. 

For  work  with  pressure   spots,  FlG  58 

bristles    of  various   sizes  may  be 

fastened  to  wooden  handles  by  means  of  sealing-wax,  or 
they  may  be  held  in  screw  clutches  which  fit  into  the 
handle  shown  in  Fig.  58.  A  clutch  for  this  purpose 
is  made  by  splitting  a  screw  and  putting  the  bristles  be- 
tween the  two  parts  of  the  screw.  The  screw  should  be 
made  in  the  form  of  a  cone.  When  a  nut  is  screwed  up 
on  this  taper,  the  sides  of  the  screw  will  be  drawn  together 
and  will  firmly  grasp  the  bristle. 

C — SUPPLEMENTARY   EXPERIMENTS 

Experiments  dealing  with  the  relativity  of  tempera- 
tures can  be  readily  prepared  by  using  dishes  of  warm 
and  cold  water.  The  observation  is  so  closely  related  to 
the  facts  of  common  experience  that  no  detailed  discussion 
of  the  matter  is  necessary. 


120        PSYCHOLOGICAL  EXPERIMENTS 

For  the  second  supplementary  experiment,  prepare  a 
series  of  light  corks  which  are  equal  to  each  other  in 
weight  but  differ  in  size,  and  ascertain  by  tests  which  one 
will  give  the  greatest  apparent  pressure. 

Experiments  on  the  tongue  can  be  made  by  drying  the 
surface  thoroughly  and  afterward  applying  drops  of  the 
substance  with  which  the  organ  of  taste  is  to  be  stimulated 
by  means  of  a  camers-hair  brush. 

One  test  for  sensitivity  of  the  skin  to  which  reference 
is  not  made  in  the  Laboratory  Manual  is  the  test  for  sensi- 
tivity to  pain.  The  apparatus  for  such  a  test  is  known  as 
an  algometer.  It  is  virtually  an  inverted  spring  balance, 
and  consists  in  a  hollow  wooden  cylinder  which  has  a 
coiled  spring  inside.  Against  this  coiled  spring  there  is  a 
piston  which  extends  out  beyond  the  end  of  the  wooden 
cylinder.  The  end  of  the  piston  is  held  against  the  part 
of  the  skin  which  is  to  be  tested,  and  the  wooden  cylinder 
which  serves  as  a  handle  is  now  pressed  downward  toward 
the  skin.  The  pressure  on  the  cylinder  acts  upon  the  piston 
through  the  spring  and  tends  to  push  the  piston  against 
the  skin  with  as  much  force  as  is  exerted  by  the  coiled 
spring  within.  If  a  scale  is  marked  on  the  wooden  cylinder 
and  a  pointer  is  attached  to  the  piston,  this  pointer  will  tend 
to  travel  up  the  scale  as  the  pressure  is  exerted  on  the 
piston,  showing  how  much  the  spring  is  brought  into  play. 
The  amount  of  pressure  necessary  to  produce  pain  at  any 
given  point  can  thus  be  read  off  directly  from  the  scale 
as  it  would  be  read  on  a  spring  balance. 


EXERCISE  IX 

A — APPARATUS   AND   PROCEDURE 

For  the  first  part  of  this  exercise  a  simple  tracing  may 
be  made  by  laying  the  hand  on  a  piece  of  paper  and  out- 
lining its  form  with  a  pencil.  The  outline  should  be  sup- 
plied with  lines  to  indicate  the  positions  of  the  knuckles, 
and  certain  of  the  prominent  features  of  the  hand  and 
arm.  If  it  can  be  had,  a  still  better  map  with  which  to 
work  is  a  life-sized  photograph  of  the  arm.  A  more 
elaborate  method  yet  is  to  secure  a  plaster  of  paris  cast 
of  the  arm  and  hand.  The  latter  device  is  necessary  only 
when  a  long  series  of  experiments  is  to  be  tried.  A  pho- 
tograph as  a  substitute  for  the  rough  outline  is  advan- 
tageous even  for  simple  demonstration  experiments. 

For  producing  the  sensations  in  the  first  part  of  the  ex- 
ercise a  simple  wooden  point  can  be  used.  The  points 
can  be  marked  by  ink  made  of  aniline  dye  and  water. 

As  a  means  of  supplying  the  stimulation  at  two  points 
on  the  skin  an  ordinary  drawing  compass  may  be  em- 
ployed. It  is  not  absolutely  necessary,  as  prescribed  in 
the  text,  that  the  points  should  be  made  of  hard  rubber, 
but  if  they  are  not  so  made  there  is  large  possibility  that 
the  observer  will  be  distracted  from  time  to  time  through 
the  excessive  stimulation  of  temperature  spots  on  the  skin. 
Even  with  a  compass,  additional  points  of  rubber  or  bone 
or  wood  may  easily  be  fastened  over  the  metallic  points, 
and  thus  the  difficulty  which  might  otherwise  arise  through 
excessive  stimulation  of  the  temperature  spots  may  be 
eliminated.  If  drawing  compasses  are  employed,  it  will 

121 


122        LABORATORY  EQUIPMENT  FOR 

be  necessary  for  the  experimenter  to  measure  the  distance 
between  the  points  by  comparison  with  a  scale. 

It  is  obviously  more  convenient  to  have  the  measure 
directly  connected  with  the  points,  so  that  when  an  adjust- 
ment is  made  a  direct  reading  of  the  distance  of  the  points 
from  each  other  can  be  seen  at  a  glance.  Fig.  59  represents 
a  simple  apparatus  very  similar  to  the  one  that  was  em- 
ployed by  Weber  in  his  experiments.  The  long  bar  A  is 
graduated  into  millimeters.  One  point  is  directly  con- 
nected with  the  extremity  of  the  graduated  bar.  Over 
the  bar  there  travels  an  adjustable  arm  which  can  be 
placed  at  any  desired  distance  from  the  fixed  point.  The 


Fio.  69 

distance  between  the  two  points  can  now  be  read  directly 
on  the  scale.  Such  an  apparatus  is  known  as  an  aesthesi- 
ometer. 

Certain  refinements  can  be  introduced  into  an  apparatus 
of  this  sort.  Thus,  instead  of  using  hard  rubber  points 
Von  Frey  has  suggested  that  bristles  be  used  which 
shall  be  of  equal  thickness,  so  that  the  two  points 
can  be  pressed  against  the  skin  with  equal  intensity. 
Such  an  addition  as  this  to  the  sesthesiometer  makes  im- 
possible any  inequality  of  pressure  at  the  two  points. 
Others  have  suggested  that  the  sesthesiometer  points  be 
held  in  some  kind  of  sliding  handle  so  that  they  will 
always  rest  against  the  skin  with  the  weight  of  the  appar- 
atus. These  refinements,  however,  are  unnecessary. 


PSYCHOLOGICAL  EXPERIMENTS         123 

With  a  little  practice  the  experimenter  can  learn  to  set  the 
two  points  down  with  equal  pressure  and  with  the  great- 
est precision  in  the  matter  of  the  time  of  contact  of  the  two 
points. 

In  the  course  of  a  series  of  experiments  with  the  two 
points  it  is  customary  to  introduce  what  has  been  called 
a  confusion  experiment.  This  consists  in  stimulating 
the  observer  with  a  single  point.  It  is  sometimes  found 
that  an  observer  gives  a  judgment  two  points  when,  as  a 
matter  of  fact,  he  is  being  stimulated  only  with  a  single 
point.  This  is  doubtless  due  in  many  cases  to  the  fact  that 
other  points  on  the  skin  are  more  or  less  irritated  by  in- 
ternal conditions  or  by  after-images  of  early  tactual  stimu- 
lations. Indeed,  after  one  has  been  experimenting  for 
some  time  with  a  given  region  of  the  skin  it  is  almost  im- 
possible to  decide  whether  a  given  experience  is  the  re- 
sult of  a  present  stimulation  or  an  after-image.  These  con- 
fusion results  will  be  found  to  be  sources  of  constant  error 
especially  with  untrained  observers.  It  is  generally  well, 
in  case  these  errors  become  too  numerous,  to  begin  with  a 
distance  between  the  two  points  so  large  that  the  observer 
has  no  difficulty  whatsoever  in  recognizing  it,  and  then  to 
gradually  reduce  the  distance  until  the  two  points  are  no 
longer  clearly  recognized.  The  degree  of  certainty  in  the 
observer's  judgments  of  the  separateness  of  the  two  points 
may  also  be  considered  in  determining  the  threshold  for 
two  points.  One  fact  which  comes  out  very  clearly  from 
these  results  is  that  the  skin  threshold  is  not  a  definite  sen- 
sory matter,  but  is  rather  the  result  of  a  complex  perceptual 
discrimination. 

If  in  addition  to  the  judgment  of  separateness  the  ob- 
server is  required  to  judge  the  direction  of  two  points  or  a 
line  upon  the  skin,  it  will  be  found  that  this  judgment  of 
direction  is  vague  in  the  extreme,  especially  in  untrained 


124        LABORATORY  EQUIPMENT  FOR 

parts  of  the  skin.     More  investigation  of  this  matter  can 
readily  be  made  by  the  methods  here  described. 

In  the  part  of  this  exercise  where  it  is  required  to  use 
lines  instead  of  points,  the  simplest  means  is  to  prepare  a 
series  of  cardboard  lines.  These  lines  should  be  cut  at 
lengths  varying  from  a  single  millimeter  to  any  desired 
length.  More  convenient  than  cardboard  lines  will  be 
found  a  system  of  thin  lines  made  of  hard  rubber,  varying 


FIG.  60 
From  an  article  by  Henri,  in  the  "Archives  de  Physiologic,"  1893,  pp.  619-627 

in  length,  as  do  the  cardboard  lines,  from  a  single  milli- 
meter to  lengths  of  from  5  to  6  centimenters. 


B — RESULTS 


Results  of  experiments  in  localization  when  single 
points  are  touched  are  shown  in  Fig.  60  and  also  in  the 
article  by  Pillsbury  in  the  American  Journal  of  Psychology, 
1895,  pp.  42-56. 


PSYCHOLOGICAL  EXPERIMENTS         125 

The  results  in  millimeters  of  the  sesthesiometer  experi- 
ment on  three  observers  were  as  follows: 


Observer  A 

Observer  B 

Observer  C 

Arm  

24 

7 
2 

27 
6 
1 

30 

8 
1 

14 
5 

3 

13 
5 

1 

15 

4 
2 

31 

8 
2 

27 
9 

32 
10 
2 

Thumb  
Finsrer.  . 

When  a  continuous  line  is  used,  it  will  be  found  that  it 
is  distinguished  from  a  point  when  it  is  less  than  half  as 
long  as  the  distance  which  must  lie  between  two  points 
in  order  that  they  may  be  distinguished  as  two. 


C — SUPPLEMENTARY   EXPERIMENTS 

Distances  across  the  arm  are  always  recognized  earlier 
than  distances  in  longitudinal  directions. 

The  supplementary  experiments  on  different  parts  of 
the  body  and  on  the  effects  of  practice  require  no  new 
apparatus  or  methods  of  procedure. 

If  a  point  is  moved  across  the  skin  it  will  be  found  that 
the  fact  of  movement  can  usually  be  recognized  before 
the  point  has  moved  over  the  distance  required  for  the  dis- 
crimination of  two  sesthesiometer  points.  The  fact  that 
perceptual  discrimination  of  different  stimulations  can  be 
more  readily  made  during  the  movement  of  the  point  has 
been  dwelt  upon  by  certain  writers  as  clear  evidence  that 
the  perception  of  motion  is  a  separate  process  from  that 
of  general  spatial  discrimination.  Elaborate  devices  have 
been  constructed  for  moving  points  across  the  surface  of 
the  skin  at  a  uniform  rate.  These  devices  have  usually 
been  supplied  with  means  of  varying  the  rate  from  very 
rapid  to  very  slow.  They  consist  in  principle  of  a  moving 
carriage  that  carries  a  pointer  which  rests  with  its  full 


126        LABORATORY  EQUIPMENT  FOR 

weight  upon  the  skin.  The  weight  of  such  a  point  can  be 
regulated  by  adding  to  the  natural  weight  of  the  pointer 
or  by  counterbalancing  it  so  as  to  make  it  lighter  than  it 
would  be  if  it  rested  with  its  full  weight  upon  the  skin. 
For  the  purposes  of  ordinary  experimentation  much  pro- 
ductive observation  can  be  made  by  using  a  wooden  point 
and  moving  it  with  the  hand,  not  attempting  to  employ 
the  more  elaborate  forms  of  apparatus. 

Many  experiments  with  the  semicircular  canals  have 
been  tried  upon  animals.  The  canals  have  been  de- 
stroyed in  various  ways  and  the  animal's  behavior  after 
the  disturbance  of  its  canals  has  been  carefully  observed. 
Certain  pathological  human  cases  also  serve  for  similar 
experiments.  Experiments  with  normal  human  beings 
can  be  tried  by  directly  stimulating  the  canals.  If  an 
electrode  is  applied  to  the  outer  surface  of  the  skull  di- 
rectly back  of  the  pinna,  effects  may  sometimes  be  pro- 
duced of  slight  dizziness  or  in  some  cases  movements  of 
the  head  may  be  induced  which  are  analogous  to  the  cor- 
rective movements  on  the  part  of  animals  when  abnormal 
conditions  of  stimulation  are  produced  through  vivisec- 
tion in  the  canals.  Such  experiments  by  stimulation  are, 
however,  not  agreeable  and  are  hardly  suitable  for  general 
experimental  courses.  A  better  method  of  demonstration 
and  experiment  for  general  classes  consists  in  observing 
the  effect  upon  the  general  recognition  of  bodily  position 
when  the  excitation  in  the  canals  is  unusual.  Thus,  let 
an  observer  stand  with  closed  eyes,  and  point  directly  in 
front  of  himself.  Now  let  him  take  three  or  four  steps  to  a 
neighboring  wall  or  blackboard  where  he  is  required  to 
indicate  the  point  which  seems  to  him  to  be  directly  in 
front  of  the  original  position  from  which  he  started.  This 
experiment  should  be  repeated  several  times  in  order  to 
determine  the  variations  which  will  appear  under  these 


PSYCHOLOGICAL  EXPERIMENTS         127 

undisturbed  conditions.  After  the  average  error  of  point- 
ing out  a  position  which  is  directly  in  front  has  been 
ascertained,  let  the  experiment  be  repeated  by  the  same 
observer  with  the  head  turned  sharply  in  some  unusual 
direction.  Thus,  let  the  observer  hold  the  head  with  the 
left  ear  as  near  to  the  left  shoulder  as  possible  or,  con- 
versely, with  the  right  ear  near  the  right  shoulder,  or  let 
the  head  be  thrown  back  as  far  as  possible,  or  let  the  neck 
be  bent  forward  as  far  as  possible.  It  will  be  found  in 
these  cases  that  the  points  selected  on  the  blackboard 
after  several  steps  forward  differ  decidedly  from  the 
points  indicated  in  the  earlier  experiments.  There  may 
be  involved  in  these  experiments  factors  other  than  the 
sensations  from  the  semicircular  canals.  The  strain  upon 
the  muscles  of  the  neck  and  the  effect  of  a  changed  posi- 
tion of  the  whole  head  are  undoubtedly  to  be  considered 
in  explaining  the  unusual  direction  of  movement. 

Measurements  of  the  ability  to  recognize  changes  in 
the  position  of  the  body  can  also  be  made  by  means  of  a 
tipping  and  rotating  table.  The  observer  lies  on  such  a 
table  and  is  gradually  tipped  so  that  the  head  rises  and  the 
feet  are  lowered,  and  record  is  made  of  the  point  where  he 
first  recognizes  the  change  in  position  from  the  starting- 
point.  Again  the  table  is  rotated  so  that  the  observer's 
head  moves  clockwise  or  counter-clockwise,  and  the  angle 
is  measured  through  which  he  must  move  in  order  to  recog- 
nize the  fact  of  movement  and  the  direction.  Such  meas- 
urements as  these  probably  deal  with  changes  in  the  pres- 
sure of  the  lymphatic  fluids  in  the  semicircular  canals. 
They  may  also  include  certain  skin  sensations.  Much 
will  depend  upon  the  rate  at  which  the  movement  is  made. 


EXERCISE  X 

A — APPARATUS  AND   PROCEDURE 

The  simplest  means  of  securing  weights  for  this  experi- 
ment is  to  take  cartridge  shells  and  ordinary  shot  and  load 
the  shells  so  that  they  are  as  heavy  as  desired.  Other 
forms  of  cylinders  can  be  prepared  consisting  of  hard 
rubber  cylinders  or  metallic  cylinders.  The  cylindrical 
form  is  distinctly  advantageous  for  all  of  the  work  because 
cylinders  can  always  be  picked  up  in  the  same  way  by  the 
observer.  Hard  rubber  is  better  than  metal  as  the  latter 
introduces  temperature  sensations. 

These  weighted  cylinders  can  be  most  readily  presented 
to  the  observer  by  means  of  a  small  rotating  table.  The 
arm  of  the  observer  is  supported  above  this  rotating  table 
within  easy  reach  of  the  weights  placed  upon  it.  The  ex- 
perimenter operates  the  table,  bringing  first  one  weight 
and  then  the  other  under  the  observer's  hand.  If  no  such 
rotating  table  as  this  is  provided,  the  experimenter  may 
place  the  arm  of  the  observer  in  a  convenient  position  and 
set  the  weights  successively  under  the  hand. 

Methods  of  treating  the  results  of  such  tests  are  given  in 
the  text  of  the  Laboratory  Manual. 

Faint  sounds  can  be  most  simply  produced  by  means 
of  a  small  body  which  is  allowed  to  fall  against  a  plate 
of  glass  or  metal.  A  convenient  body  for  this  purpose  is  a 
small  pith-ball.  A  suitable  scale  may  be  fastened  at  the 
side  of  a  glass  plate,  and  the  pith-ball  held  in  a  funnel  or 
taken  in  a  pair  of  forceps  which  can  be  brought  to  any 
desired  height  on  the  scale.  When  the  funnel  or  forceps  are 

128 


PSYCHOLOGICAL  EXPERIMENTS         129 

opened,  the  pith-ball  will  fall  through  a  known  distance 
to  the  plate  of  glass  or  metal  below.  The  sound  which 
it  produces  will  be  sufficiently  faint  to  allow  a  considerable 
range  of  variation  either  in  the  height  of  the  fall  or  in  the 
distance  of  the  object  from  the  ear,  and  a  measurement 
can  thus  be  secured  of  the  intensity  of  sound  just  neces- 
sary for  auditory  recognition.  If  the  apparatus  is  moved 
further  and  further  away  from  the  ear  in  order  to  produce 
a  fainter  sound,  it  is  not  necessary  to  have  a  scale  connected 


FIG.  61 
From  the  catalogue  of  Zimmermann,  Leipzig,  Germany 

with  the  glass  plate.  The  forceps  or  funnel  may  he  held 
in  a  fixed  position  at  a  certain  height  above  the  glass. 
The  distance  through  which  the  pith-ball  falls  will  thus  be 
in  every  case  the  same,  the  variation  in  intensity  of  sound 
being  produced  by  the  distance  of  the  apparatus  from  the 
observer's  ear.  Fig.  61  shows  an  elaborate  device  of  this 
kind. 

A  second  form  of  audiometer  consists  in  a  telephone 
which  is  connected  with  the  secondary  coil  of  an  induction 


130        LABORATORY  EQUIPMENT  FOR 

coil.  The  secondary  coil  is  made  adjustable  so  that  it  can 
be  varied  in  its  position  with  reference  to  the  primary  coil. 
The  current  which  is  to  pass  through  the  primary  coil  is 
controlled  by  means  of  a  make  and  break  key.  If  now 
the  secondary  coil  is  placed  at  a  given  distance  from  the 
primary,  and  the  current  in  the  primary  is  made  and  broken, 
a  sound  will  be  produced  in  the  telephone.  If  the  sound 
is  of  sufficient  intensity  for  the  observer  to  recognize  it, 
the  intensity  of  the  current  in  the  secondary  coil  should  be 
reduced  by  moving  this  coil  further  away  from  the  primary, 


Fig.  62 

and  the  experiment  should  be  repeated  until  the  distance 
is  found  at  which  the  observer  is  unable  to  recognize  the 
faint  sound  produced  in  the  telephone.  The  distance 
between  the  coils  constitutes  a  measure  of  the  auditory 
sensitivity. 

Physicians  use  a  much  simpler  test  than  either  of  these 
in  determining  for  diagnostic  purposes  the  sensitivity  of 
the  ears.  They  use  the  tick  of  a  watch  or  a  faint  whisper, 
and  measure  the  threshold  in  terms  of  the  distance  to  which 
the  sound  must  be  removed  from  the  ear  in  order  that  it 
may  become  too  faint  to  be  recognized. 


PSYCHOLOGICAL  EXPERIMENTS         131 

A  simple  form  of  photometer  is  shown  in  Fig.  62.  Two 
sources  of  light  are  set  up  on  the  blocks  A  and  B.  Con- 
venient sources  of  light  for  this  purpose  are  candles.  Be- 
tween the  two  sources  of  light  is  a  shield  D.  There  is  set 
up  at  C  a  rod  which  will  cast  shadows  on  the  screen  as 
shown  at  S  and  S'.  The  blocks  A  and  B  should  be  moved 
by  the  experimenter  until  the  shadows  S  and  S'  seem  to 
the  observer  just  noticeably  different  in  intensity.  The 
difference  in  the  distance  of  the  two  blocks  from  the  rod 
can  be  determined,  and  this  distance  constitutes  a  measure 
of  the  just  perceptible  difference  in  illumination  necessary 
for  the  observer's  recognition.  If  now  the  total  illumina- 
tion of  the  room  is  changed,  it  will  be  found  that  the  dis- 
tance of  the  blocks  from  the  rod  necessary  to  produce  a 
just  perceptible  difference  in  the  shadows  has  also  changed. 
In  order  to  control  easily  the  total  illumination  of  the 
room  as  required  in  this  experiment,  the  apparatus 
should  be  set  up  in  a  room  that  can  be  darkened. 

Other  photometers  are  constructed  in  such  a  way  that 
light  from  different  sources  falls  upon  two  neighboring 
plates  of  milk  glass.  Such  plates  of  milk  glass  should  be 
separated  from  each  other  by  an  opaque  metal  strip. 
They  should  be  placed  so  that  they  can  both  be  seen  by 
the  observer  at  the  same  time.  The  sources  of  light  should 
now  be  so  adjusted  that  the  illumination  of  one  plate  of 
glass  can  be  recognized  as  just  noticeably  greater  or  less 
than  the  illumination  of  the  other  plate.  The  principle 
here  employed  consists  in  a  direct  examination  of  the  illu- 
minated surface,  rather  than  in  the  comparison  of  shad- 
ows as  in  the  photometer  shown  in  Fig.  62.  In  the  second 
form  of  photometer,  as  well  as  in  the  shadow  photo- 
meter, the  measurement  is  made  in  terms  of  the  distance  of 
the  sources  of  light.  These  measurements  can  be  reduced 
to  an  absolute  physical  basis  by  recognizing  the  general 


132        LABORATORY  EQUIPMENT  FOR 

physical  formula  that  the  intensity  of  lights  is  inversely 
proportional  to  the  square  of  their  distances. 

Other  forms  of  photometers  are  numerous  and  can  be 
arranged  without  difficulty.  The  principle  of  all  such  in- 
struments is  sufficiently  illustrated  in  the  one  or  the  other 
of  the  forms  described. 


C — SUPPLEMENTARY   EXPERIMENTS 

In  the  first  supplementary  experiment  the  comparison 
of  differences  is  suggested.     Such  a  comparison  can  be 

worked  out  with  auditory  sen- 
sations by  arranging  four  balls 
so  that  they  can  be  dropped 
from  different  heights.  A  cer- 
tain difference  in  height  be- 
tween balls  1  and  2  will  produce 
a  known  difference  in  the  in- 
tensity of  their  sounds.  Balls  3 
and  4  are  also  dropped  from 
known  heights,  the  difference 
between  their  heights  being  ad- 
justed in  the  course  of  succes- 
sive trials  to  satisfy  the  listening 
observer.  The  difficulty  in  car- 
rying out  this  experiment  arises 
from  the  great  difficulty  of  pro- 
viding balls  that  are  just  alike 
and  uniform  plates  on  which  the 
balls  may  fall.  Furthermore, 
the  balls  must  be  dropped  by  some  sort  of  mechanical 
device  which  shall  prevent  them  from  rotating  and  shall 
be  noiseless.  Such  an  elaborate  apparatus  has  been 
worked  out  in  the  I^eipzig  Laboratory  and  is  described  in 


FIG.  63 

From  Wundt's  "Grundziige   der 

physiologischen  Psychologie," 

5th  Ed.,  Vol.  I,  p.  513 


PSYCHOLOGICAL  EXPERIMENTS         133 

full  in  the  Philosophische  Studien,  1892,  Vol.  VII.  The 
essential  part  of  the  apparatus,  namely  that  by  means 
of  which  the  ball  is  dropped  without  rotation,  is  shown 
in  Fig.  63. 

It  is  much  simpler  to  determine  the  threshold  for  just 
perceptible  difference  in  sounds.  Fig.  64  represents  a 
pendulum  apparatus  designed  for  this  experiment.  Two 
pendulums  with  ivory  bulbs  at  their  ends  are  so  pivoted 
that  they  can  be  lifted  to  suitable  distances  in  front  of 
scales  and  then  allowed  to  descend  against  a  block.  As 
the  pendulum  rebounds  it  is  caught  either  by  the  hand  or 


FIG.  64 
From  the  catalogue  of  Diedrich,  Goettingen,  Germany 

by  a  felt  catch.  The  second  pendulum  is  dropped  in 
like  manner  through  a  slightly  different  distance,  and 
the  second  sound  thus  produced  is  to  be  compared  by  the 
observer  with  that  produced  by  the  first  fall.  If  the 
difference  is  not  perceived,  the  experiment  should  proceed, 
the  difference  between  the  two  distances  through  which 
the  pendulums  fall  being  slightly  increased. 

An  apparatus  known  as  an  olfactometer  is  used  for  ex- 
periments with  intensities  of  odors.  Let  a  glass  tube  TT 
be  supplied  with  a  nasal  bulb  as  represented  in  Fig.  65  at 
N.  This  tube  is  held  by  a  handle.  Over  the  tube  T  is 
slipped  a  second  larger  tube  MM,  which  is  lined  on  the 


134        LABORATORY  EQUIPMENT  FOR 

inside  with  a  layer  of  paraffin.  The  tube  T  is  represented 
in  the  figure  with  its  outer  tube  MM  in  such  a  position 
that  the  air  drawn  into  the  nose  during  inspiration  will 
have  been  exposed  for  a  time  to  the  paraffin  surface  of 
MM  and  will  have  taken  up  any  odor  which  MM  tends 
to  give  out.  If  MM  is  drawn  further  along  T,  a  greater 
surface  will  be  exposed  and  the  odor  will  be  relatively 
more  intense.  The  amount  of  surface  exposed  in  MM 
is  accordingly  a  measure  of  the  intensity  of  the  odor  en- 
tering the  nose. 

Experiments  on  taste  have  been  carried  on  by  stimu- 
lating the  tongue  with  solutions  of 
various  degrees  of  saturation. 

Experiments     have     sometimes 
been  tried  with  stimuli  which  are 
undergoing    very  gradual  change; 
no.  es  that  is,  instead   of  requiring   the 

observer  to  compare  two   clearly 

different  intensities  of  pressure,  a  given  pressure  is  modified 
gradually.  The  threshold  of  discrimination  will  be  differ- 
ent from  that  which  results  from  a  sudden  change.  The 
same  type  of  experimentation  has  been  worked  out  for 
gradually  varying  sounds.  The  devices  for  producing 
gradual  variations  in  weight  are  in  principle  a  form  of 
balance  upon  which  weights  of  greater  intensity  are  gradu- 
ally imposed.  Flowing  water  has  l>een  used  to  increase 
the  weight  of  the  pressure  gradually;  the  sliding  of  a  weight 
along  a  counterbalance  arm  has  also  been  employed. 
For  purposes  of  change  in  the  quality  of  tones  the  tone- 
variator  of  Stern,  described  on  page  111,  may  be  employed. 
The  determination  of  pressure  thresholds  has  been 
touched  on  in  discussing  pressure  points  (page  119). 
An  elaborate  piece  of  apparatus  for  producing  and  meas- 
uring pressures  is  shown  in  Fig.  66.  The  small  ivory 


PSYCHOLOGICAL  EXPERIMENTS         135 

point  St  is  brought  into  contact  with  some  part  of  the  skin 
by  raising  the  arm  H2.  This  lever  may  be  raised  by  some 
form  of  clockwork  which  will  determine  its  rate.  As  the 
lever  H2  rises  it  brings  into  action  the  coil  spring  Mz 
gradually  increasing  the  pressure  at  St.  By  means  of  the 
scale  the  degree  of  pressure  can  be  directly  read.  The 
initial  position  of  the  lever  H 2  can  be  regulated  by  the 
screw  S  and  the  height  of  the  apparatus  after  it  is  clamped 
in  position  can  be  adjusted  by  means  of  the  screw  Ms. 
A  principle  similar  to  Weber's  law  can  be  demonstrated 


FIG.  66 
From  the  catalogue  of  Zimmermann,  Leipzig,  Germany 

for  the  recognition  of  the  length  of  lines.  If  a  series  of 
lines  differing  from  each  other  in  length  is  prepared  in  a 
manner  analogous  to  that  described  above  for  the  weights, 
experiments  by  the  method  of  right  and  wrong  cases  may 
be  carried  out.  Thus,  if  a  line  10  cm.  long  is  compared 
with  a  line  10.5  cm.  long,  and  a  line  2  cm.  long  is  com- 
pared with  one  2.1  cm.  long,  the  methods  and  results  will 
be  analogous  to  those  described  above  for  weights. 

Another  method  may  be  used  for  lines  which  can  not 


136        PSYCHOLOGICAL  EXPERIMENTS 

be  employed  for  weights.  In  this  case  the  observer  may 
be  required  to  draw  a  line  which  seems  to  him  to  be  equal 
to  a  given  line,  or  he  may  be  required  to  draw  a  line  which 
is  just  noticeably  shorter  or  just  noticeably  longer  than 
the  given  line.  Again,  the  observer  may  be  given  a  certain 
line  and  may  be  asked  to  cut  off  that  portion  of  the  line 
which  seems  to  him  to  be  equal  to  a  standard.  This  ex- 
periment has  been  elaborated  as  a  typical  experiment  in 
quantitative  determination  of  psychical  processes  in  the 
introduction  of  the  Laboratory  Manual  and  need  not  be 
worked  out  further  at  this  point.  (See  Laboratory  Man- 
ual, pp.  3-10.) 


EXERCISE  XI 

A — APPARATUS   AND   PROCEDURE 

A  simple  tambour  is  represented  in  Fig.  67.  A  bowl 
B  opens  at  the  side  into  a  tube  S.  The  bowl  is  covered 
over  the  top  by  means  of  a  thin  rubber  membrane 
which  is  held  in  position  in  this  form  of  tambour  by  a 
tightly  fitting  metallic  ring  R.  Rubber  suitable  for  tam- 
bours can  be  secured  at  any  place  where  dentists  secure 
their  supply  of  rubber  dam.  The  rubber  is  sometimes 
tied  around  the  bowl  which  is  constructed  with  a  groove 
below  its  edge.  In  order  to  insure  an  air-tight  contact, 
the  edge  of  the  bowl  may  be  prepared  for  the  reception  of 


FIG.  67 
From  Professor  Porter's  catalogue  of  Harvard  Physiological  Apparatus 

the  rubber  membrane  by  giving  it  a  thin  coat  of  wax. 
Ordinary  beeswax  serves  the  purpose  very  well.  The 
rubber  should  be  stretched  as  little  as  possible  so  as  to 
leave  it  free  to  move  with  the  least  possible  resistance. 
From  the  hollow  stem  S  a  thick  walled  rubber  tube  may 
be  carried  to  any  point  desired  and  a  second  tambour 
may  be  attached  to  the  other  end  of  the  conducting  tube, 
the  two  acting  in  harmony,  one  to  receive,  the  other  to 
record  the  movement.  In  order  to  avoid  loss  of  energy 
through  the  elasticity  of  rubber  tubing,  it  is  advantageous 

137 


138         LABORATORY  EQUIPMENT  FOR 

where  the  connection  is  a  long  one,  to  insert  a  glass  tube 
in  place  of  the  rubber  wherever  possible.  Any  pressure 
which  is  exerted  on  the  rubber  surface  of  one  of  the  tam- 
bours will  force  air  into  the  other  tambour  and  will  pro- 
duce a  movement  in  the  rubber  of  this  second  tambour. 
The  advantages  of  this  arrangement  are  that  movements 
may  be  taken  on  one  tambour  at  any  point  desired  and 
may  be  conveyed  to  a  second  point  where  they  can  be 


FIG.  68 
From  the  catalogue  of  C.  H.  Stocking  Co.,  Chicago 

recorded  on  suitable   surfaces    prepared    to   receive  the 
record. 

A  record  of  the  movement  of  a  tambour  surface  can  be 
made  by  means  of  a  lever  attached  to  the  surface  of  the 
rubber  as  shown  in  the  Fig.  67  at  W,  P,  L.  This  lever  may 
be  of  an  extremely  simple  form.  A  wire  coil  W  may  be 
wound  around  a  pipe  S.  At  P  the  wire  carries  a  fulcrum 
and  a  lever  L.  This  latter  is  connected  with  the  rubber 
of  the  tambour  by  a  light  angle  of  metal,  C.  Any  move- 
ment of  the  rubber  surface  will  be  transmitted  to  the 
lever  and  magnified  at  the  end  of  the  lever.  The  degree 


PSYCHOLOGICAL  EXPERIMENTS         139 

in  which  the  movement  is  thus  magnified  will  depend  on 
the  distance  between  P  and  (7,  and  C  and  the  end  of  the 
lever.  PC  may  be  varied  by  sliding  W  along  S. 

A  more  satisfactory  form  of  lever  is  shown  in  the  tam- 
bour represented  in  Fig.  68.  It  consists  of  a  post  H 
which  carries  a  horizontal  bar  A  which  can  be  set  back- 
ward and  forward  by  means  of  the  set-screw  X.  The 
horizontal  rod  A  is  supplied  at  its  end  with  a  fork  L  and  a 
pair  of  point  bearings.  The  fork  can  be  adjusted  up  and 
down  by  the  set-screw  K  which  acts  against  a  spring. 
The  point  bearings  in  L  carry  a  cross  rod  to  which  the 
lever  is  attached,  as  represented  at  F.  The  lever  F  is 
fastened  to  the  rubber  surface  of  the  tambour  by  means 
of  a  light  metal  rod  which  has  fastened  at  its  bottom  a  thin 
metallic  plate.  In  some  cases  the  rod  which  connects  the 
lever  with  the  rubber  is  forked  at  the  top.  The  lever  is 
held  in  position  in  this  fork  by  means  of  a  small  rubber 
band  which  passes  around  the  prongs  of  the  fork  and  over 
the  lever.  Suitable  rubber  bands  for  this  purpose  may 
be  made  from  a  small,  pure  rubber  tube.  Such  a  small, 
pure  rubber  tube  may  be  cut  off  in  thin  sections  with  a  pair 
of  scissors,  and  these  sections  will  supply  the  band  desired. 
The  plate  at  the  bottom  of  the  rod  is  fastened  to  the  rubber 
by  means  of  a  drop  of  wax.  This  wax  can  be  melted  by 
bringing  a  hot  metal  bar  in  contact  with  the  upper  sur- 
face of  the  plate. 

It  will  be  found  convenient  to  mount  the  tambour  on 
a  standard  which  is  quite  separate  from  the  bowl  or  from 
the  recording  lever.  This  can  be  done  as  indicated  in 
Fig.  68,  where  the  bowl  is  connected  with  a  standard  by 
means  of  an  arm  W.  This  arm  can  be  mounted  on  a 
spring  S,  which  is  fastened  at  the  end  opposite  the  point 
where  it  carries  W  in  a  clamp  by  means  of  which  it  can  be 
fastened  to  a  standard.  Connected  also  with  the  clamp 


140        LABORATORY  EQUIPMENT  FOR 

there  may  be  a  set-screw  0,  which  presses  against  the 
spring  S.  If  now  the  clamp  is  held  firmly  in  position  and 
the  set-screw  is  operated  backward  and  forward,  the  whole 
tambour  with  its  recording  points  can  be  adjusted  back  and 
forth  so  as  to  be  brought  nearer  the  surface  on  which  the 
record  is  to  be  made,  or  removed  further  from  this  surface. 
The  advantage  of  such  a  screw  adjustment  is  that  the  re- 
cording point  can  be  delicately  adjusted  to  any  required 
degree  of  pressure  upon  the  surface  upon  which  it  is  to 
record.  Such  delicate  adjustment  will  be  found  to  be  in- 
dispensable if  the  records  are  to  be  taken  with  as  little 
friction  as  possible. 


Fio.  60 
From  the  catalogue  of  Verdin,  Paris,  France 

A  great  variety  of  tambours  are  supplied  by  makers. 
Fig.  69  represents  a  form  in  which  the  bowl  instead  of  the 
lever  is  adjusted.  This  figure  shows  very  well  the  plate 
which  connects  the  lever  and  the  rubber. 

It  is  desirable  that  the  levers  used  with  tambours 
should  be  as  light  as  possible.  Most  very  light  rods  have 
the  disadvantage  of  vibrating  whenever  they  move.  A 
hollow  cylindrical  rod  is  least  subject  to  this  objection,  and 
fortunately  nature  has  provided  light  hollow  cylindrical 
rods  in  abundance  in  straws.  The  best  straw  for  tam- 
bours is  fine,  clean  rye  straw.  If  this  can  not  be  easily  se- 
cured, a  substitute  can  be  found  at  almost  any  florist's 


PSYCHOLOGICAL  EXPERIMENTS         141 

where  sheaves  of  an  Italian  grain  will  be  found.  This 
imported  Italian  grain  is  used  as  a  miniature  substitute 
for  sheaves  of  wheat.  The  straws  are  fine  and  straight. 
They  are  somewhat  heavier  than  rye  straws  but  serve 
very  well. 

An  important  part  of  a  tambour  is  its  recording  point. 
This  should  be  at  once  flexible  enough  to  insure  so  far  as 
possible  a  reduction  of  the  friction  against  the  record  sur- 
face, and  it  should  be  rigid  enough  to  insure  a  clear  mark. 
As  will  be  stated  later,  the  form  of  surface  mo'st  commonly 
used  in  making  records  is  a  surface  of  smoked  paper. 
Points  for  tracing  on  such  surfaces  may  be  made  of  parch- 
ment. The  parchment  should  be  cut  with  sharp  scissors 
to  a  point,  and  the  point  should  be  slightly  curled,  so  as  to 
press  against  the  smoked  paper  surface  with  the  elasticity 
of  its  curve.  Such  a  parchment  point  may  be  fastened 
to  the  end  of  the  straw  by  a  drop  of  wax.  Or  the  end  of 
the  straw  may  be  split,  the  parchment  inserted  in  the  slit 
thus  prepared,  and  the  whole  bound  with  a  fine  silk 
thread.  Another  very  satisfactory  point  can  be  made 
by  using  celluloid,  which  can  be  treated  in  the  same 
way  as  the  parchment.  Pendulum  ribbon  makes  a  good 
metal  point.  Heavy  tinfoil  may  be  used. 

Tambours  can  be  used  in  various  combinations.  It 
will  be  convenient  to  speak  of  a  tambour  supplied  with  a 
lever  and  a  recording  point  as  a  recording  tambour.  Tam- 
bours which  have  no  levers  attached  may  be  variously 
attached  to  the  finger  or  head  or  other  part  of  the  body 
and  will  be  called,  because  of  their  function  of  receiving 
the  movement,  receiving  tambours. 

It  is  often  convenient  in  practical  work  to  be  able  to 
introduce  air  into  a  tambour  without  pulling  apart  the 
connections.  A  convenient  device  for  doing  this  is  a  short 
metal  tube  which  is  inserted  in  the  rubber  tube  leading 


142        LABORATORY  EQUIPMENT  FOR 

from  receiving  tambour  to  recording  tambour.  Such  a 
tube  is  represented  in  Fig.  70.  At  A  is  a  fine  opening 
communicating  when  open  with  the  outer  atmosphere 
and  the  air  system  inside  of  the  tambours  Under  ordi- 
nary circumstances  A  is  kept  closed  by  the  small 
stopper  BB1B",  which  is  pressed  down  against  it  by  the 
spring  S.  When  it  is  desired  to  open  A  the  finger  presses 
at  B\ 

One  of  the  most  fertile  sources  of  annoyance  in  work- 
ing with  tambours  is  to  find  that  they  are  not  air-tight. 
It  is  frequently  necessary  for  the  student  who  is  to  use 
tambours  to  renew  the  rubber  covering.  Indeed,  it  is 
usually  better  for  him  to  begin  any  experiment  with  an 
entirely  new  rubber  on  the  tambour.  It  will  be  found 


advantageous  in  every  laboratory  to  have  the  material 
necessary  for  setting  up  tambours  at  hand  in  such  form 
as  to  be  easily  accessible  to  the  student.  A  box  can  be 
prepared  containing  the  smaller  parts  of  the  tambours, 
a  supply  of  rubber,  a  supply  of  strong  thread,  a  pair  of 
scissors  and  beeswax.  If  the  tambour  is  to  be  used  only 
a  short  time  it  is  often  convenient  to  fasten  the  rubber 
tambour  by  means  of  a  wire  instead  of  thread.  A  fine 
wire  and  a  pair  of  pinchers  should  accordingly  be  added  to 
the  equipment.  If  the  wire  is  drawn  firmly  around  the 
tambour  it  can  be  fastened  by  twisting  it  up  with  the 
pinchers.  The  disadvantage  with  the  wire  connection  is 
that  it  very  soon  cuts  through  the  rubber. 

After  securing  a  recorder,  a  surface  must  be  provided  for 


PSYCHOLOGICAL  EXPERIMENTS         143 

taking  the  record.  In  order  that  the  movements  of  the 
tambour  levers  may  be  fully  recorded,  the  surface  must 
offer  as  little  friction  as  possible  and  it  must  be  moved  for- 
ward so  that  when  one  part  of  the  record  is  completed 
an  unused  portion  of  the  receiving  surface  may  be  substi- 
tuted for  the  part  on  which  the  recorder  has  been  tracing, 
and  a  new  phase  of  the  movement  be  recorded.  The 
movement  of  the  surface  also  aids  in  reducing  the  friction. 
We  may,  therefore,  begin  our  description  with  the  moving 
device  which  is  known  as  a  kymograph. 

A  variety  of  kymographs  are  in  use.  The  simplest  con- 
sists of  a  large  brass  cylinder  about  15  cm.  in  diameter. 
Such  a  brass  cylinder  or  drum,  as  it  is  called,  should  have 
as  smooth  a  surface  as  can  be  provided.  It  should  be 
turned  in  an  accurate  lathe  so  as  to  be  a  perfect  cylinder, 
and  it  should  be  kept  polished  by  means  of  buffing  appar- 
atus so  that  its  surface  may  at  all  times  be  as  nearly  as 
possible  free  from  irregularities.  It  is  desirable  that  this 
drum  should  be  rotated  at  a  uniform  rate.  The  prob- 
lem of  securing  regularity  of  movement  is  a  problem 
which  has  resulted  in  a  number  of  clock-work  devices  and 
electrical  devices.  If  one  wishes  the  highest  degree  of  ac- 
curacy he  will  find  that  all  these  devices  are  subject  to  some 
variations;  the  effort  to  drive  the  drum  at  a  uniform  rate 
is  therefore  at  times  abandoned,  in  which  case  it  becomes 
necessary  to  trace  upon  the  receiving  surface  a  standard 
time-line.  Any  irregularities  in  the  movement  of  the  drum 
will  be  indicated  by  means  of  this  standard  time-line,  and 
the  results  of  the  record  to  be  studied  can  be  measured 
in  terms  of  the  standard  time-line  rather  than  in  terms  of 
the  movement  of  the  drum. 

Of  the  devices  for  driving  the  drum  at  a  uniform  rate, 
the  clock-work  devices  are  the  simplest.  A  cheap  and 
very  satisfactory  clock-work  device  was  prepared  by  Pro- 


144        LABORATORY  EQUIPMENT  FOR 

fessor  Porter  of  the  Harvard  Medical  School,  in  the  ky- 
mograph which  is  supplied  with  the  Harvard  physiologi- 
cal apparatus.  It  consists  of  clock-work  shown  in  the 
accompanying  Fig.  71.  The  drum  is  carried  in  a  vertical 
position  and  driven  by  a  friction  contact  between  the  foot 
of  the  drum  and  the  shaft  which  is  connected  with  the 
clock-work.  The  whole  is  regulated  with  reference  to  its 
speed  by  a  fan  governor  shown  in 
the  figure.  The  fan  governor  con- 
sists of  a  flat  piece  of  metal  which, 
in  its  rotation,  strikes  the  air  and 
offers,  because  of  the  constancy  of 
the  pressure  of  the  atmosphere,  a 
uniform  resistance  to  the  clock- 
work. Fans  of  various  sizes  are 
provided  with  the  apparatus. 

More  elaborate  kymographs  are 
made,  the  best  clock-work  kymo- 
graph being  that  which  bears  the 
name  of  the  physiologist  Ludwig. 
This  kymograph  is  supplied  by 
Zimmermann,  in  Leipzig,  Germany. 
It  is  represented  in  Fig.  72,  and 
consists  of  an  elaborate  clock-work, 
which  by  means  of  the  coupling 
and  uncoupling  of  certain  of  its 
gearings  gives  a  wide  range  of  adjustment  of  speed.  The 
speed  of  the  drum  may  also  be  regulated  by  means  of  a  fan 
governor  which  consists  in  this  case  of  a  pair  of  wings 
which  spread  out  against  springs  because  of  the  centrifugal 
force  exerted  during  rotation.  When  springs  of  a  given 
strength  are  placed  in  position  in  this  governor,  the  fans 
of  the  governor  tend  to  spread  out  to  a  certain  extent,  de- 
pending upon  the  balance  between  centrifugal  force  and 


Fio.  71 


From  Professor  Porter's 
catalogue  of  Harvard 
Physiological  Apparatus 


PSYCHOLOGICAL  EXPERIMENTS         145 

the  tension  of  the  springs,  and  thus  maintain  a  uniform 
rate  of  movement  in  the  kymograph.  The  drum  may  be 
placed  either  in  the  vertical  or  horizontal  position  as  is 
most  convenient  for  the  record.  The  figure  shows  at  the 
left  a  tripod  standard  with  a  disk  and  rotating  arm  and 
contacts  to  be  used  in  securing  regular  time  intervals  for 


FIG.  72 
From  the  catalogue  of  Zimmermann,  Leipzig,  Germany 

the  purposes  of  experimentation  with  time  perception. 
This  part  of  the  apparatus  will  be  referred  to  again  in 
connection  with  the  supplementary  experiments  under 
Exercise  XXIII. 

For  ordinary  laboratory  purposes  it  will  be  found  con- 
venient to  use  a  simple  drum  not  connected  with  clock- 
work and  to  drive  this  with  an  electric  motor.  Such  an 


146         LABORATORY  EQUIPMENT  FOR 

arrangement  can  not  be  relied  upon,  it  is  true,  to  give  as 
uniform  speed  as  clock-work,  but  it  does  not  need  to  be 
wound  during  the  course  of  the  experiment  and  it  is  a 
very  much  cheaper  arrangement  than  any  which  is  driven 
by  clock-work.  It  is  capable  of  a  great  variety  of  modi- 
fications, and  two  or  three  drums  of  this  sort  will  make 
possible  a  very  large  number  of  combinations  for  re- 
cording purposes.  The  drum-shaft  should  be  supplied 
with  either  a  belt-wheel  or  a  cog-gear.  The  cog  is  better 
for  certain  purposes  since  it  provides  against  the  possi- 
bility of  any  slipping,  but  for  most 
purposes  the  simple  belt  is  alto- 
gether adequate.  By  means  of  a 
series  of  pulleys  and  countershafts 
such  as  are  represented  in  Fig.  73, 
any  rate  of  movement  in  the  drum 
can  be  secured.  Commonly  two 
or  three  intermediate  pulleys  will 
be  placed  between  the  drum-shaft 
and  the  electric  motor.  The  fan 
motor  referred  to  under  Exercise 
III,  (page  52)  serves  very  well  to 
drive  this  drum. 

A  number  of  motors  have  been 

devised  which  are  so  regulated  that  they  move  at  uni- 
form speed.  The  oldest  of  these  was  designed  by  Helm- 
holtz  and  is  known  as  the  Helmholtz  rotation  apparatus. 
It  consists  of  the  ordinary  parts  of  an  electric  motor  with 
an  additional  part  which  regulates  the  amount  of  current 
that  is  supplied  to  the  motor.  This  regulator  consists 
of  an  arm  which  can  move  outward  by  centrifugal  force 
wherever  the  shaft  of  the  motor  is  set  into  rotation  with 
sufficient  speed.  As  soon  as  this  centrifugal  arm  moves 
outward  from  the  shaft  it  breaks  an  electric  contact  and 


FIG.  73 

From  the  catalogue  of  Zim- 
tnermann,  Leipzig,  Germany 


PSYCHOLOGICAL  EXPERIMENTS         147 

introduces  a  certain  amount  of  resistance  into  the  electric 
circuit  which  drives  the  motor.  The  reduction  of  the  cur- 
rent tends  to  reduce  the  speed  of  the  motor.  As  soon  as 
the  speed  is  reduced  the  centrifugal  arm  falls  back  again 
against  the  shaft  and  the  extra  resistance  is  cut  out. 
The  motor  once  more  begins  to  move  more  rapidly,  the 
centrifugal  arm  again  moves  away  from  the  shaft  and  in-, 
troduces  the  resistance,  and  so  on.  The  point  of  regular 
rotation  in  this  apparatus  is  reached  when  the  centrifugal 
arm  makes  a  continuous  light  tapping  due  to  its  constant 
movement  away  from  the  shaft  and  back  again.  Recently 
devices  have  been  worked  out  for  regulating  a  motor  by 
means  of  a  tuning-fork. 

The  drum  and  its  motor  being  provided,  the  next  step 
consists  in  the  preparation  of  a  suitable  surface  for  taking 
the  record.  A  strip  of  heavy  glazed  paper,  no  wider  than 
the  drum,  should  be  pasted  around  the  drum.  In  doing 
this  care  should  be  taken  to  bring  the  paper  as  smoothly 
in  contact  with  the  drum  at  all  points  as  possible,  and  to 
paste  it  under  such  tension  that  it  shall  be  held  firmly  in 
position  against  the  metallic  surface.  The  paste  should 
not  be  applied  to  the  surface  of  the  drum  but  along  the  line 
of  contact  of  the  two  ends  of  the  paper.  Instead  of  pasting 
a  sheet  of  paper  on  a  single  drum,  it  is  very  convenient, 
especially  if  a  long  record  is  to  be  taken,  to  carry  a  belt 
of  paper  between  two  drums,  as  indicated  in  Fig.  74.  If 
a  drum  A  is  driven  by  means  of  clock-work  or  by  means 
of  an  electric  motor,  it  will  drive  the  drum  B  which  does 
not  need  to  be  connected  with  the  driving  device  except 
through  the  belt  of  paper  C.  In  practical  operation  this 
belt  of  paper  can  be  made  as  long  as  the  strength  of  the 
paper  will  permit.  Belts  of  paper  70  feet  long  have  been 
utilized,  although  care  must  be  taken  in  the  use  of  such  a 
long  belt  not  to  bring  too  great  a  strain  upon  it  at  any 


148        LABORATORY  EQUIPMENT  FOR 

part  of  the  belt  during  the  process  of  taking  or  fixing  the 
record.     The  adjustment  of  the  belt  of  paper  on  these 


FIG.  74 


two  drums  requires  some  manipulation.     In  the  first  place, 
the  two  drums  must  be  in  alinement  and  the  ends  of  the 


PSYCHOLOGICAL  EXPERIMENTS         149 

paper  must  be  carefully  pasted  so  as  to  make  a  true  joint 
in  the  paper.  The  two  drums  will  probably  need  to  be 
adjusted  after  being  set  up.  They  may  be  brought  into 
approximate  position  and  the  belt  slowly  rotated.  If 
the  belt  tends  to  run  off  the  drums,  the  drums  should  be 
readjusted  with  reference  to  each  other  on  the  following 
principles:  If  the  belt  tends  to  run  to  the  right  or  left  on 
the  remote  drum,  the  near  drum  should  be  set  in  a  direc- 
tion opposite  to  that  in  which  the  paper  tends  to  run. 
Thus,  if  the  paper  runs  toward  the  right  of  the  remote 
drum,  the  drum  near  at  hand  should  be  moved  gradually 
toward  the  left.  If  the  movement  is  made  gradually,  the 
paper  can  usually  be  brought  into  a  position  of  equilibrium 
very  readily.  Rapid  movements  are  unfavorable  to  the 
adjustment.  If  instead  of  running  off  of  the  remote  drum, 
the  paper  tends  to  run  to  the  right  or  left  on  the  drum  near 
at  hand,  this  tendency  may  be  corrected  by  moving  one  or 
the  other  end  of  the  drum  toward  or  away  from  the  remote 
drum.  The  belt  travels  in  the  direction  of  least  tension,  so 
that  if  the  belt  tends  to  run  off  at  the  right  side  of  the  drum 
near  at  hand,  it  indicates  that  there  is  less  tension  on  the 
right-hand  side  of  the  belt  than  on  the  left-hand  side. 
The  right-hand  end  of  the  drum  should,  therefore,  be  drawn 
away  from  the  more  remote  drum  so  as  to  increase  the  ten- 
sion of  the  belt  on  the  right  side.  With  a  little  practice 
the  experimenter  can  learn  to  manipulate  the  belt  easily, 
and  to  adjust  it  so  that  it  will  run  smoothly  and  in  a  given 
part  of  the  two  drums.  The  most  important  condition 
for  this  desirable  result  is  the  careful  pasting  of  the  strip 
of  paper  at  the  outset  of  the  experiment. 

When  the  belt  is  adjusted  or  the  paper  pasted  upon  the 
kymograph,  the  next  step  is  to  lay  on  a  coat  of  lampblack. 
A  variety  of  forms  of  combustion  can  be  employed  for  pro- 
ducing a  layer  of  lampblack.  In  every  case  the  heat 


150        LABORATORY  EQUIPMENT  FOR 

should  be  applied  to  the  paper  only  where  the  paper  is  in 
contact  with  the  drum.  The  metal  drum  serves  to  con- 
duct away  the  heat  and  prevents  the  paper  from  burning. 

The  finest  grade  of  lampblack  can  be  produced  by  burn- 
ing camphor  under  the  paper  and  rotating  the  drum  at  a 
considerable  speed,  carrying  the  paper  through  the  smoke. 
Camphor  is  more  expensive  than  some  of  the  other  sub- 
stances which  can  be  employed.  Ordinary  illuminating 
gas  gives  a  very  good  fine  layer  of  lampblack.  The  form 
of  flame  which  is  most  advantageous  is  one  which  gives  the 
least  possibility  of  complete  combustion  of  the  illuminat- 
ing gas.  A  wide  flame  supplied  with  gas  through  large 
holes  is  the  most  desirable  flame  for  this  purpose.  The 
drum  should  be  rotated  so  as  to  draw  the  flame  underneath 
the  drum,  and  the  flame  should  be  held  in  such  a  position 
that  it  is  in  contact  with  the  paper  only  at  the  red,  upper 
part  of  the  flame.  Coarser  and  less  desirable  forms  of 
lampblack  may  be  produced  by  burning  under  the  paper 
kerosene  or  even  turpentine.  The  latter  produces  very 
rapidly  a  thick  layer  of  lampblack,  but  it  is  coarse  and 
therefore  not  so  advantageous  for  delicate  work  as  some 
of  the  other  forms  mentioned.  Automatic  devices  for 
smoking  strips  of  paper  have  from  time  to  time  been  de- 
scribed; they  are  all  very  complicated  and  can  be  dispensed 
with,  especially  if  one  uses  belts  instead  of  single  sheets  of 
paper. 

When  the  tambour  point  has  been  allowed  to  trace  on 
this  lampblack  surface  and  the  record  has  thus  been  se- 
cured, it  may  be  made  permanent  by  shellacing  or  varnish- 
ing the  lampblack  surface.  The  most  convenient  device  for 
shellacing  or  varnishing  consists  in  the  apparatus  repre- 
sented in  Fig.  75.  A  tray  T  is  mounted  in  a  table  S  and 
may  be  covered  when  not  in  use  by  a  cover.  At  the  bot- 
tom of  the  tray  a  rubber  tube  is  carried,  as  indicated  by 


PSYCHOLOGICAL  EXPERIMENTS        151 

R,  to  a  bottle  which  contains  the  liquid  varnish  or  shellac. 
This  bottle  should  be  suspended  by  means  of  a  string 
which  passes  through  the  pulley  P  and  is  fastened  at  the 
bottom  to  a  pedal  M.  When  it  is  desired  to  shellac  a  strip 
of  paper,  the  foot  is  placed  upon  the  pedal  M,  and  the 
bottle  containing  the  varnish  or  shellac  is  raised  to  a  level 
higher  than  the  tray  T,  and  the  varnish  runs  into  the  tray 
T.  As  soon  as  the  foot  is  removed  from  the  pedal,  the 


FIG.  75 


bottle  sinks  to  a  level  lower  than  the  tray  and  the  varnish 
runs  back  into  the  bottle.  It  is  not  necessary  to  immerse 
the  paper  taken  from  the  kymograph  in  the  varnish  or 
shellac.  It  is  enough  that  the  varnish  or  shellac  be  brought 
into  contact  with  the  back  or  unsmoked  surface  of  the 
record.  This  is  accomplished  by  drawing  the  strip  of 
paper,  after  it  is  removed  from  the  drum,  through  the  tray 
so  that  its  unsmoked  surface  comes  in  contact  with  the 


152        LABORATORY  EQUIPMENT  FOR 

shellac.  The  shellaced  paper  may  be  hung  in  a  holder 
above  the  tray  and  allowed  to  drip  into  the  tray,  thus 
saving  all  the  unused  fluid.  If  it  is  desired  to  keep  the 
records  as  permanent  records,  it  will  be  necessary  to  pro- 
vide a  good  quality  of  shellac.  If  the  record  is  merely  for 
temporary  use  any  thin  transparent  varnish  will  serve  the 
purpose. 

If  the  record  is  made  on  a  long  belt  as  shown  in  Fig.  74, 
the  simplest  method  of  fixing  it  is  to  shellac  the  belt  on  the 
unsmoked  surface  while  it  is  still  on  the  drums.  A  bottle 

of  shellac  is  provided  with  a 
bent  tube  in  the  cork,  as 
shown  in  Fig.  76.  From  this 
a  small  stream  is  poured  on 
the  back  or  unsmoked  sur- 
face of  the  long  strip  and 
spread  by  means  of  a  large 
brush  so  as  to  cover  all  parts 
of  the  paper.  If  this  process 
76  of  shellacing  is  undertaken 

with  some   deliberation  there 

will  be  no  danger  of  the  paper  being  torn  or  of  covering 
the  drums  with  wet  shellac.  If  the  work  must  be  done 
hurriedly,  the  drums  are  likely  to  be  covered  with  the 
shellac  and  it  will  be  necessary  to  clean  the  drums  from 
time  to  time  by  buffing  them.  It  will  be  especially  neces- 
sary to  guard  against  the  tearing  of  the  paper,  which  is, 
of  course,  very  much  weaker  when  wet  with  the  shellac 
than  it  is  when  dry. 

The  record  which  is  secured  by  allowing  a  tambour 
point  to  trace  upon  a  moving  surface  will  depend  for  its 
length  upon  the  length  of  the  movement  recorded  and  the 
rate  of  movement  of  the  record  surface.  If  this  surface 
is  moving  rapidly,  the  record  of  a  given  movement  will  be 


PSYCHOLOGICAL  EXPERIMENTS         153 

long  drawn  out;  if  the  surface  moves  slowly,  the  record  will 
be  much  condensed.  If  the  surface  moves  at  a  uniform  rate, 
the  various  parts  of  the  record  will  be  directly  comparable; 
if  the  surface  moves  at  an  irregular  rate,  comparison  of  the 
various  parts  of  the  record  can  not  be  directly  made.  It 
is  often  desirable  to  state  the  results  from  records  obtained 
in  this  way  in  absolute  terms  and  to  provide,  as  indicated 
in  an  earlier  paragraph,  against  the  possible  irregularities 
in  the  movement  of  the  receiving  surface.  In  such  cases, 
a  time-line  from  a  vibrator  of  known  rate  may  be  traced 
on  the  paper  along  with  the  tambour  record. 
The  simplest  method  of  securing  a  standard  time-line 


P 

FIG.  77 
From  the  catalogue  of  C.  H.  Stoelting  Co.,  Chicago 

is  to  use  a  Jaquet  chronometer  manufactured  by  Verdin, 
in  Paris.  This  is  a  small  stop-clock  with  a  lever  attach- 
ment which  moves  every  second  or  every  fifth  of  a  second 
according  as  it  is  set  for  the  one  interval  or  the  other. 
The  lever  can  be  made  to  trace  directly  on  a  kymograph. 
Another  method  of  securing  a  time  record  is  to  attach 
a  point  of  pendulum  ribbon,  similar  to  that  described  in 
connection  with  the  tambour,  to  a  tuning-fork  or  other 
vibrator  and  hold  this  point  during  the  vibration  of  the 
fork  or  rod  against  the  record  surface.  If  a  very  short 
unit  of  time  is  desired,  a  100-vibration  fork  or  a  500- 
vibration  fork  may  be  used.  The  difficulty  with  such 
a  contrivance  is  that  the  time  record  is  very  short,  or  else 


154        LABORATORY  EQUIPMENT  FOR 

the  experimenter  must  devote  himself  to  keeping  the  fork 
in  motion.  A  device  for  keeping  the  fork  in  motion  is  pro- 
vided in  the  electric  fork,  which  operates  on  the  same 
principle  as  the  vibrator  described  on  page  99.  Such  a 
fork  is  represented  in  Fig.  77.  It  consists  of  an  ordinary 
fork  mounted  on  a  frame  and  having  between  its  prongs  an 
electromagnet.  The  current  for  this  electromagnet  enters 
through  the  fork  and  passes  from  the  fork  to  the  magnet, 
whenever  contact  is  made  between  the  spring  S  and  the 
plate,  which  can  be  adjusted  by  means  of  the  screw  P. 
S  and  P  will  be  in  contact  whenever  the  prongs  of  the  fork 
vibrate  outward.  As  soon  as  S  and  P  come  together,  the 
current  passes  from  the  fork  through  the  magnet  and  back 
to  the  battery.  The  magnet  will  now  attract  the  prongs 
of  the  fork  inward  with  a  strong  impulse.  The  rate  at 
which  the  prongs  of  the  fork  respond  to  the  attraction  of 
the  magnet  will  be  determined  by  the  fork's  natural  rate  of 
vibration.  The  energy  for  the  movement  will  be  supplied 
by  the  magnet.  As  soon  as  the  prongs  of  the  fork  vibrate 
inward  in  response  to  the  attraction  of  the  magnet,  the 
contact  between  S  and  P  will  be  broken,  the  electromagnet 
will  cease  to  attract  the  fork,  and  by  its  own  elasticity  the 
fork  will  tend  to  vibrate  outward  again.  In  vibrating 
outward  the  contact  at  S  and  P  is  established  again  and  the 
process  is  indefinitely  repeated. 

An  electric  fork  has  two  uses;  it  may  be  used  directly  to 
make  a  tracing  on  a  kymograph  or  it  may  be  used  indi- 
rectly to  make  and  break  an  electric  current,  this  current 
in  turn  being  used  to  make  the  record  on  the  drum. 

If  the  fork  is  to  be  used  directly,  a  point  is  attached  to 
the  end  of  one  of  the  prongs,  and  the  fork  is  held  in  contact 
with  the  drum.  A  convenient  means  of  holding  the  fork 
is  the  clamp  shown  in  Fig.  78.  The  shaft  R  passes  through 
a  hole  drilled  through  the  base  on  which  the  electric  fork 


PSYCHOLOGICAL  EXPERIMENTS         155 

is  mounted.  The  fork  is  held  firmly  on  this  shaft  by 
means  of  the  screw  S.  This  rod  R  is  clamped  by  the  screw 
/  to  a  second  rod  P,  which  is  hollow  and  fits  over  the  third 

rod  T,  which  is  held  by  the 
standard.  From  P  and  T 
two  arms  project,  as  shown 
in  0  and  Q.  Between  these 
arms  is  the  set-screw  N  which 
controls  the  distance  between 
them.  T  is  clamped  to  a 
holder,  the  fork  is  fastened  at 
FIG.  78  RS ,  and  by  means  of  N  the 

From  the "  Studies  from  the  Yale  Psy-  •+•  f     j.^       frvrL-    rna\r    KA 

choiogicai  Laboratory,"  Vol.  iv     position  ot   me  torK  may  oe 

nicely   adjusted    up  or  down 

so  as  to  regulate  the  pressure  of  its  point  against  the 
smoked  paper. 

If  the  fork  is  to  be  used  indirectly,  a  marker  is  required. 
A  simple  marker  is  represented  in  Fig.  79.  An  electro- 
magnet ra  is  connected  in  series  with  the  electric  tuning- 
fork.  A  current  passes  through  ra  every  time  a  contact 
is  made  at  the  fork.  Directly  in  front  of  the  metallic 
core  e  of  the  magnet  ra,  is  placed  a  spring  point  a.  The 
marker  a  is  held  by  its  own  elasticity  away  from  the  magnet, 
but  not  far  enough  away  to  be  beyond  the  range  of  attrac- 
tion when  the  current  passes 
through  the  magnet.  As  a  re- 
sult, the  marker  a  moves  toward 
the  magnet  whenever  a  current 
passes  through  the  coil  and  os- 
cillates in  the  opposite  direction  FlQ  79  *" 
when  the  current  in  the  coil  is 

interrupted .  Very  often  the  spring  which  draws  the  marking 
point  away  from  the  magnet  is  a  coil  spring.  The  moving 
point  a  is  made  to  trace  on  the  smoked  paper  surface. 


156        LABORATORY  EQUIPMENT  FOR 

Various  forms  of  markers  have  been  devised.  In  gen- 
eral if  one's  equipment  is  limited,  it  is  better  to  procure  a 
small  marker.  This  can  be  used  for  either  a  slow  or  a 
rapid  record,  whereas  a  heavy  marker  has  too  great  in- 
ertia for  rapid  vibrations. 

The  principle  of  the  electric  tuning-fork  and  of  the  in- 
terrupter described  on  page  99  may  be  elaborated  so  as 
to  give  any  desired  rate  of  motion  and  any  desired  strength 


Fio.  80 
From  the  catalogue  of  Zimmermann,  Leipzig,  Germany 

of  current.  One  of  the  most  elaborate  instruments  con- 
structed on  this  principle  is  the  Kronecker  interrupter. 
This  interrupter  is  supplied  with  mercury  contacts  for 
making  and  breaking  the  current.  It  is  also  supplied  by 
means  of  an  additional  pair  of  contacts  with  the  means  of 
making  and  breaking  a  current  entirely  separate  from 
that  which  drives  the  vibrating  rod.  It  is  supplied  with 
a  system  of  tubes  by  means  of  which  the  mercury  con- 
tacts are  kept  clean  by  a  flowing  stream  of  water  that 


PSYCHOLOGICAL  EXPERIMENTS         157 

passes  over  these  contacts.  This  stream  of  water  is  sup- 
plied from  a  small  reservoir  which  stands  a  little  above 
the  mercury  contacts.  From  this  reservoir  the  water  is 
conducted  by  tubes  directly  across  the  mercury.  The  pla- 
tinum needles  pass  through  the  water  and  into  the  mercury, 
the  contact  not  being  completed  until  the  needles  reach 
the  mercury.  If  it  is  desired  to  secure  intervals  of  time 
of  a  second  or  longer,  a  pendulum  may  conveniently  be 
used.  A  contact  pendulum  manufactured  for  this  purpose 
and  giving  series  of  contacts  for  any  interval  from  one 
half  of  a  second  to  a  minute  is  shown  in  Fig.  80.  With 
each  oscillation  of  the  pendulum  the  dial  is  advanced  one 
degree.  An  outer  series  of  metallic  posts  is  so  arranged 
that  with  each  movement  of  the  dial  a  post  comes  in  con- 
tact with  the  catch.  Other  series  of  posts  on  the  dial  are 
separated  by  longer  intervals.  The  catch  may  be  adjusted 
so  as  to  connect  with  any  series  desired.  The  catch  con- 
trols an  electric  current  which  is  thus  regulated  by  the 
clock  for  any  long  interval  desired.  A  simple  contact  may 
be  arranged  with  any  pendulum  by  allowing  it  to  sweep 
through  a  meniscus  of  mercury.  In  such  a  case  one  wire 
should  be  connected  with  the  pendulum,  the  other  with 
the  mercury. 

It  is  sometimes  possible  and  desirable  with  markers 
which  record  long  intervals  and  consequently  move  slowly, 
to  make  a  record  by  means  of  a  pencil  or  pen  on  a  paper 
which  is  not  smoked.  The  pencil  used  for  such  purposes 
is  mounted  at  the  end  of  a  flexible  metal  strip  which  presses 
it  against  the  paper  and  is  at  the  same  time  sufficiently 
elastic  to  avoid  excessive  friction.  A  pen  may  be  similarly 
mounted.  The  best  form  of  pen  is  one  which  feeds  out 
the  ink  through  a  capillary  opening.  A  glass  tube  drawn 
to  a  fine  point  makes  a  very  good  pen.  Metallic  pens 
with  holes  of  very  small  caliber  can  also  be  used. 


158        LABORATORY  EQUIPMENT  FOR 

The  records  which  are  made  by  a  tambour  can  be  used 
not  merely  for  the  purpose  of  determining  the  duration  of 
movements  but  also  for  the  purpose  of  studying  the  in- 
tensity and  form  of  these  movements.  The  intensity  and 
form  are,  however,  by  no  means  as  directly  recorded  as 
the  rate,  for  the  tension  of  the  tambour  rubbers  increases 
rapidly  after  the  rubber  has  been  stretched  even  very 
slightly.  The  last  part  of  the  movement  of  a  tambour 
lever  represents  not  merely  the  energy  necessary  to  lift 
the  lever  itself,  but  in  addition  the  energy  necessary  to 
stretch  the  rubber.  For  this  reason  the  quantitative  use 
of  a  tambour  record  to  show  the  amount  of  movement  in- 


Fig.81 

volves  complex  corrections.  In  a  general  way  a  higher 
movement  means  a  greater  amount  of  energy  of  move- 
ment, but  the  amount  of  energy  expended  is  not  directly 
proportional  to  the  movement  of  the  tambour  recorder. 
A  record  is  presented  in  Fig.  81  showing  a  regular  time- 
line from  a  100-vibration  fork.  A  second  line  shows  the 
tambour  record  of  an  upward  and  downward  finger  move- 
ment which  is  executed  as  rapidly  as  possible.  It  will 
be  seen  that  the  successive  finger  movements  differ  from 
each  other  in  intensity  and  in  regularity  of  form  as  well 
as  duration. 

It  remains  to  mention  in  connection  with  the  kymo- 
graph and  its  accessories,  standards  for  carrying  the  vari- 


PSYCHOLOGICAL  EXPERIMENTS         159 

ous  recording  pieces.  The  simplest  standards  consist 
merely  of  heavy  metallic  bases  into  which  are  set  rods. 
The  best  bases  for  such  standards  are  heavy  tripods. 
More  convenient  than  these  simple  standards  is  one  which 
can  be  raised  or  lowered  by  means  of  a  screw.  Such  screw 
standards  may  be  connected  with  kymograph  drums  so 
as  to  move  the  tracing  points  automatically  as  the  drum 
revolves. 


EXERCISE  XII 

A — APPARATUS    AND    PROCEDURE 

The  simplest  contrivance  for  securing  records  of  the 
rate  of  the  heart-beat  consists  in  a  recording  tambour,  such 
as  was  described  under  the  last  exercise,  and  a  rubber  tube 
connecting  this  recording  tambour  with  a  thistle  tube  such 
as  is  shown  in  Fig.  82.  The  large  end  of  the  thistle  tube 
should  be  placed  against  the  skin  of  the  neck  just  over 
the  carotid  artery  and  should  be  held  in  position  by  rods 
and  clamps  fastened  to  a  table  or  portable  base.  The 
skin  of  the  neck  serves  as  a  cover  for  the  thistle  tube,  which 
is  thus  converted  into  a  tambour,  and  the  pulse  of  the 
carotid  artery  will  at  intervals  compress  the  air  in  the 

thistle   tube,  with   the   result 
that    the    recording   tambour 
will  be  set  in  motion  at   the 
,  same  rate  as  the  pulse.     The 

difficulty    with   this    arrange- 
ment is  that  any  movement  of 

the  reactor's  head  and  any  motion  of  swallowing  or  un- 
usual breathing  will  change  the  pressure  of  the  air  within 
the  thistle  tube  and  complicate  the  pulse  record.  The 
first  difficulty  can  be  very  largely  overcome  by  fixing  the 
head  in  the  head-rest  already  described  under  Exercise 
II,  page  31.  No  easy  means  of  overcoming  the  diffi- 
culty that  arises  from  swallowing  can  be  provided.  It  is 
better  for  this  reason  to  utilize  the  pulse  in  the  radial 
artery. 

The  radial  pulse  is  not  strong  enough  and  the  skin  of  the 

160 


PSYCHOLOGICAL  EXPERIMENTS         161 

wrist  is  not  smooth  enough  to  allow  the  use  of  a  thistle  tube, 
and  a  special  contrivance  must  be  provided  for  recording 
this  pulse.  The  simplest  contrivance  that  can  be  used  is  a 
cork  fastened  to  an  ordinary  recording  tambour.  If  one 
end  of  the  cork  is  fastened  to  the  rubber  surface  of  the 
tambour  by  a  drop  of  wax,  and  the  whole  tambour  is  held 
in  a  clamp  in  such  a  position  that  the  free  end  of  the  cork 


FIG.  83 


presses  against  the  radial  artery,  a  record  may  be  taken 
with  a  recording  tambour  which  will  correspond  in  rate 
and  in  intensity  to  the  rate  and  intensity  of  the  movement 
induced  in  the  receiving  tambour  by  the  pulse. 

Fig.  83  shows  a  more  elaborate  contrivance  for  record- 
ing the  radial  pulse.  A  spring  $,  with  a  small  plate  P,  is 
brought  by  means  of  a  frame  F  into  contact  with  the  radial 
artery  at  the  point  P.  Bands  are  provided  which  will 
hold  the  frame  firmly  against  the  arm.  These  bands  are 
not  represented  in  the  figure.  Passing  through  a  wire 


162        LABORATORY  EQUIPMENT  FOR 

hook  L  connected  with  the  spring  is  a  small  rod  which 
is  fastened  perpendicularly  to  the  long  bar  W.  At  the 
other  end  of  H7is  a  long  arm  K ,  which  serves  to  magnify  the 
movements  communicated  by  the  spring  at  L.  This  en- 
larging lever  may  be  made  to  carry  a  point  which  will  trace 
directly  upon  a  smoked  surface,  or  it  may  be  connected 
with  other  enlarging  devices  before  the  tracing  is  made. 
A  very  effective  enlarging  device  is  represented  in  Fig. 
83.  The  end  of  the  lever  K  is  made  into  a  loop  as  shown 
at  N.  Through  this  is  allowed  to  pass  a  rod  which  is 
weighted  on  a  short  perpendicular  arm  by  a  small  weight  X. 
This  weighted  rod  has  its  fulcrum  at  R. 
At  the  end  of  its  lower  long  arm  J  is  a 
loose  joint  with  a  tracing  point  0.  The 
weight  draws  the  rod  RJ  into  the  posi- 
tion of  rest  against  the  loop  N.  If  the 
loop  N  is  moved,  the  rod  will  be  moved 
with  it  and  the  record  can  be  taken  at 
0.  The  result  will  be  that  the  move- 
ments of  the  lever  K  are  a  second  time 
enlarged  by  this  additional  leverage. 
In  the  use  of  such  an  apparatus,  which  is  technically 
known  as  a  sphygmograph,  care  must  be  taken  to  have 
the  relation  between  the  arm  and  the  recording  surface 
perfectly  constant.  If  the  arm  is  allowed  to  move  in  any 
degree,  the  tracing  at  the  end  of  the  pointer  will  be  affected 
by  the  arm  movement  as  well  as  by  the  movement  of  the 
pulse,  and  a  source  of  error  will  thus  be  introduced  in  the 
readings. 

A  simple  device  for  holding  the  arm  in  a  fixed  position 
consists  of  an  arm-rest  made  up  of  two  U-shaped  brackets 
shown  in  Fig.  83a,  through  which  the  arm  is  allowed  to 
pass  and  lie  in  a  comfortable  position.  The  hand  should 
clasp  firmly  the  holder,  which  can  be  adjusted  by  means  of 


PSYCHOLOGICAL  EXPERIMENTS         163 

a  rod  to  any  desired  level.     A  sphygmograph  attached  to 
the  arm  held  in  such  a  rest  as  this  can  be  adjusted  so  as 


FIG.  84 
From  the  catalogue  of  Zimmermann,  Leipzig,  Germany 

to  trace  upon  a  drum,  which  has  been  set  in  the  proper 
position  with  reference  to  the  arm-rest. 

There  are  other  sphygmographs.  In  some  of  them  the 
movement  of  the  spring  which  presses  against  the  pulse  is 
communicated  to  a  tambour  and  thus  recorded  on  a 
kymograph.  Such  a  sphygmograph  is  shown  in  Fig.  84. 
P  presses  against  the  artery  with  a  pressure  controlled  by 


FIG.  85 


the  spring  M .  As  P  moves  up  and  down  it  acts  upon  the 
tambour  shown  in  the  figure.  The  frame  is  to  hold  the 
apparatus  on  the  arm. 


164        LABORATORY  EQUIPMENT  FOR 

B — RESULTS 

Fig.  85  shows  a  typical  record  from  the  sphygmograph. 
The  following  table  shows  the  change  in  heart-beats 
resulting  from  the  various  forms  of  excitation : 

1.  Multiply  31  by  17. 

2.  Multiply  27  by  13. 

3.  Strong  disagreeable  odor. 

4.  Pleasant  odor. 


Average   number  of 
heart-beats  in  5  se- 
lected periods  of   10 
seconds  during  2  min- 
utes preceding  stim- 
ulus 

Average   number  of 
heart-beats   in   each 
10  seconds  during  30 
seconds  immediately 
after  stimulus 

Average   number  of 
heart-beats  in  5  se- 
lected periods  of   10 
seconds  during  2  min- 
utes following  stim- 
ulus 

M.  V. 

M.V. 

M.V. 

1 

2 
3 
4 

14.1 
14.6 
14.3 
14.0 

0.4 
0.7 
0.3 
0.5 

15.6 
14.7 
17.3 
16.2 

0.7 
0.9 
1.1 
1.2 

15.2 
14.8 
16.1 
15.5 

1.4 
1.0 
1.3 
1.1 

C — SUPPLEMENTARY   EXPERIMENTS 

A  second  type  of  apparatus  for  securing  records  of  vaso- 
motor  changes  is  the  plethysmograph.  This  is  made  to 
enclose  some  part  of  the  body  and  record  changes  in  the 
volume  of  a  part  of  the  body  which  it  encloses. 

The  simplest  plethysmograph  is  made  for  the  finger. 
It  consists  in  a  small  glass  cylinder.  This  cylinder  has 
a  thin  rubber  hood  extending  into  it  to  receive  the  finger. 
This  rubber  hood  is  fastened  to  the  edge  of  the  cylinder 
so  that  the  whole  makes  what  may  be  called  a  hollow 
tambour.  The  finger  of  the  reactor  can  now  be  inserted 
in  the  rubber  hood,  and  the  finger  and  cylinder  are  held 
firmly  in  position  by  means  of  the  necessary  arm-rests 


PSYCHOLOGICAL  EXPERIMENTS        165 

and  clamps.  If  the  volume  of  the  finger  increases  or  de- 
creases, as  it  will  with  each  pulse-beat,  or  if  it  undergoes 
more  gradual  changes  through  the  withdrawal  of  the  blood, 
or  through  an  excessive  flow  of  blood  to  the  finger,  the  air 
between  the  wall  of  the  cylinder  and  the  rubber  hood  will 
be  driven  out  or  drawn  in  each  time  there  is  an  increase 
or  decrease  in  the  volume  of  the  finger.  If  a  recording 
tambour  is  connected  with  the  cylinder,  changes  in  the 
volume  of  the  finger  will  be  recorded. 

The  principle  employed  in  this  finger  plethysmograph 


FIG.  86 
From  the  catalogue  of  Zimmennann,  Leipzig,  Germany 

can  be  applied  to  a  larger  apparatus  for  the  arm.  Fig. 
86  represents  an  arm  plethysmograph  supplied  by  Zim- 
mermann.  The  arm  is  inserted  in  the  large  cylinder  and 
held  in  position  by  the  elbow  rest.  The  cylinder  contains 
a  large  rubber  sleeve,  and  the  space  between  this  sleeve 
and  the  walls  of  the  cylinder  is  filled  with  water.  The 
water  rises  into  the  glass  tube  extending  vertically  out  of 
the  cylinder,  and  from  this  glass  tube  connections  are  car- 
ried to  a  recording  tambour.  Rubber  sleeves  for  this 
plethysmograph  can  be  made  at  any  rubber  establishment 
by  using  a  mold  of  proper  size  made  of  polished  wood  or, 


166        LABORATORY  EQUIPMENT  FOR 

still  better,  of  glass.  The  objection  to  this  form  of  plethys- 
mograph  is  that  the  rubber  sleeve  or  sack  does  not  fit 
closely  around  the  hand,  especially  at  the  end,  and  error 
is  likely  to  be  introduced  into  the  record  through  involun- 
tary movements  of  the  fingers.  Such  movements  result 
in  changes  in  the  volume  of  the  rubber  sack,  which  are  in 
no  way  due  to  changes  in  the  volume  of  the  arm.  One 
method  of  reducing  this  error  to  its  minimum  is  to  close 
the  hand  firmly  about  some  solid  object  and  keep  it  clenched 
inside  of  the  rubber  sleeve. 

A  still  better  device  consists  in  eliminating  altogether 
the  closed  end  of  the  rubber  sleeve.  An  outer  metallic 
cylinder,  open  at  both  ends,  is  drawn  over  the  arm.  This 
cylinder  is  supplied  with  a  rubber  sack  which  is  made 
fast  at  the  ends  of  this  tube.  The  hand  thus  extends 
freely  beyond  the  rubber  sack.  If,  now,  water  is  allowed 
to  fill  the  cylinder  between  the  rubber  sack  and  the  wall 
of  the  cylinder  and  to  rise  for  a  short  distance  in  a  vertical 
tube,  similar  to  that  shown  in  Fig.  86,  a  record  can  be 
taken  as  in  the  other  cases  by  means  of  a  recording  tam- 
bour. This  form  of  plethysmograph  has  the  advantage 
over  the  finger  plethysmograph  of  including  a  larger  part 
of  the  body  and,  therefore,  insuring  a  greater  change  in 
volume.  It  has  a  decided  advantage  over  the  Zimmer- 
mann  plethysmograph  in  that  no  involuntary  hand  move- 
ments will  change  the  volume  of  the  arm. 

A  form  of  apparatus  which  has  recently  been  described 
by  Professor  Henderson  could  be  used  to  great  advantage 
in  experiments  on  the  relation  of  circulation  to  conscious 
processes.  The  apparatus,  called  a  recoil  table,  consists 
of  a  table  on  which  the  reactor  lies.  This  table  is  sus- 
pended or  supported  on  flexible  supports  so  that  it  may 
readily  swing  through  a  small  distance.  Levers  are  con- 
nected with  the  table  so  as  to  record  any  movement. 


PSYCHOLOGICAL  EXPERIMENTS         167 

Whenever  the  heart  of  a  reactor  drives  the  blood  into  the 
aorta  there  will  be  a  recoil  of  the  body,  in  accordance  with 
the  familiar  physical  principle  of  action  and  reaction,  in 
a  direction  opposite  to  that  in  which  the  heart  forced  the 
blood.  This  recoil  of  the  body  is  communicated  to  the 
table  on  which  the  reactor  lies  and  through  the  leverage  is 
recorded  on  the  kymograph. 

A  form  of  apparatus  required  in  the  third  accessory  ex- 
periment of  this  exercise  for  measuring  changes  in  the 
rate  of  intensity  or  respiration  is  known  as  a  pneumograph. 
A  very  satisfactory  pneumograph  is  represented  in  Fig. 


FIG.  87 

87.  It  consists  of  a  coiled  spring  C  twenty-five  to  forty 
centimeters  in  length,  covered  with  a  light  rubber  tube 
RR,  which  is  entirely  closed  at  one  end  and  at  the  other  end 
is  fastened  firmly  around  a  small  metallic  tube  which  per- 
mits connection  with  a  rubber  tube  leading  to  a  recording 
tambour.  From  the  ends  of  the  coiled  spring  A  and  B 
extends  a  chain  which  is  fastened  about  the  thorax  of  the 
reactor.  When  the  pneumograph  is  in  position,  the  coiled 
spring  C  should  be  under  slight  tension.  Any  change  in 
the  volume  of  the  thorax  will  result  in  a  change  in  the  ex- 
pansion of  the  coiled  spring  C,  and  as  a  result  the  volume 


168        PSYCHOLOGICAL  EXPERIMENTS 

of  the  air  column  within  the  rubber  tube  R  will  be  modi- 
fied and  the  changes  in  this  air  column  will  be  recorded  at 
the  recording  tambour.  By  using  more  than  one  pneu- 
mograph,  tracings  can  be  made  for  different  parts  of  the 
thorax  during  a  single  act  of  respiration.  By  using  at  the 
same  time  a  pneumograph  and  a  plethysmograph  or 
sphygmograph,  parallel  tracings  can  be  made  for  respira- 
tion and  the  heart  action. 

For  reasons  which  were  pointed  out  in  the  earlier  dis- 
cussion of  tambour  records  (page  158),  the  records  from 
sphygmographs,  pneumographs,  and  plethysmographs  can 
not  be  regarded  as  direct  quantitative  records  of  the  amount 
of  movement  of  the  pulse  or  lungs.  The  recoil  table  has 
a  distinct  advantage  in  this  respect,  in  that  the  amount  of 
movement  of  the  table  is  directly  proportional  to  the 
amount  of  blood  moved  at  each  heart-beat.  The  records 
from  sphygmographs,  pneumographs,  and  plethysmographs 
may,  however,  be  treated  quantitatively  so  far  as  the  rate 
and  general  intensity  of  the  movement  is  concerned. 

For  a  study  of  changes  in  the  size  of  the  pupil  of  the  eye 
the  best  method  is  to  photograph  the  eye  in  a  good  light. 
The  light  for  this  purpose  may  be  sunlight  reduced  in 
intensity  by  passing  it  through  a  screen  of  blue  glass,  the 
screen  being  of  any  thickness  necessary  to  prevent  dis- 
comfort on  the  part  of  the  reactor. 

If  the  eyes  are  not  photographed,  measurements  may 
be  taken  by  observing  the  eyes  of  the  reactor  through  a 
reading  telescope  placed  at  some  distance  in  front  of  the 
reactor. 


EXERCISE  XIII 

A — APPARATUS   AND   PROCEDURE 

The  steadiness  of  the  finger  can  be  measured  by  al- 
lowing it  to  rest  upon  the  rubber  surface  of  a  receiving 
tambour,  any  movement  of  this  tambour  being  carried  to 
the  recording  tambour  and  there  traced  upon  smoked 
paper.  The  only  precaution  required  is  that  the  pressure 
shall  not  be  so  great  as  to  bring  the  finger  into  contact  with 
the  bottom  of  the  tambour,  nor  so  light  as  to  make  no  im- 
pression on  the  rubber.  Another  somewhat  simpler  de- 
vice is  to  allow  the  finger  to  rest  on  one  end  of  a  lever 
which  is  held  in  position  by  means  of  a  fulcrum  and  traces 
at  the  end  opposite  that  which  is  in  contact  with  the 
finger,  on  a  kymograph.  Slight  movements  of  the  finger 
can  be  magnified  in  this  way  as  much  as  desired.  In  like 
fashion,  head  movements  may  be  recorded  by  connecting 
the  head  by  means  of  a  rigid  rod  with  a  receiving  tam- 
bour or  with  a  tracer  which  marks  directly  on  a  recording 
surface. 

Various  forms  of  planchettes  have  been  devised.  The 
simplest  consists  of  a  board  hung  from  the  ceiling  of  the 
room  by  a  long  string  or  wire.  A  board  thus  suspended 
by  a  long  string  can  be  moved  very  freely,  and  its  move- 
ment will  be  practically  in  a  straight  line  through  any  ordi- 
nary distance  such  as  would  be  required  for  the  experi- 
ment. Another  device  for  furnishing  a  recorder  for  hand 
or  arm,  which  can  be  moved  with  very  little  friction,  con- 
sists of  a  glass  plate  supported  on  a  second  glass  by  large 
balls,  such  as  are  used  for  ball  bearings.  After  securing  by 

169 


170        LABORATORY  EQUIPMENT  FOR 

one  of  these  means  a  surface  which  can  be  moved  with 
relatively  little  friction,  it  is  necessary  to  provide  a  tracing 
point.  This  tracing  point  should  add  as  little  as  possible 
to  the  friction  of  the  movement.  In  some  cases  a  pointer 
has  been  allowed  to  trace  upon  smoked  paper.  The  paper 
is  smoked  on  a  kymograph  and  is  spread  out  on  a  flat 
surface  under  the  pointer.  The  pointer  may  be  of  the 
simple  sort  described  in. discussing  tracing  points  for  tam- 
bours or  it  may  be  a  stylus  especially  designed  for  use 
with  the  planchette.  A  very  convenient  form  of  stylus 
consists  of  a  rod  which  passes  freely  through  a  glass  or 
metal  tube.  Such  a  stylus  always  rests  on  the  receiving 
surface  with  its  own  weight.  The  metallic  or  glass 
tube  through  which  it  passes  is  fastened  to  the 
planchette.  As  the  planchette  moves  backward 
and  forward  the  pointer  will  trace  its  movements 
on  the  smoked  paper.  The  smoked  surface  may 
be  dispensed  with  if  the  stylus  is  made  in  the 
form  of  an  ink  pen.  For  this  latter  purpose  a 
special  pen-point  must  be  provided  which  will 
trace  equally  well  in  any  direction.  The  ordinary  pen-point 
will  not  serve  because  it  traces  freely  only  in  one  direction. 
Fig.  88  represents  a  form  of  pen-point  which  answers  the 
purpose.  It  consists  of  a  small  metal  rod  turned  down 
to  a  point  into  which  a  groove  has  been  sawed  as  repre- 
sented at  G.  The  two  points  P  and  Pr  have  been  bent 
together  so  that  they  are  nearly  in  contact.  A  hole  which 
serves  as  a  reservoir  for  ink  is  drilled  at  the  upper  end  of 
the  slit  between  the  points.  The  size  of  this  reservoir  is 
determined  by  trial.  If  it  is  too  large  the  ink  is  forced  out 
too  rapidly.  If  it  is  too  small  it  requires  very  frequent  re- 
filling. Such  a  pen  as  this  should  be  prepared  for  making 
the  record  by  being  filled  with  some  thin  fluid  ink.  The 
best  ink  for  the  purpose  consists  of  a  water  solution  of  one 


PSYCHOLOGICAL  EXPERIMENTS        171 

of  the  aniline  dyes.  Such  a  pen  as  this  will  mark  freely 
in  any  direction,  and  the  amount  of  ink  it  will  carry  is  quite 
adequate  for  an  ordinary  record. 

B — RESULTS 

A  number  of  very  striking  records  of  involuntary  hand 
movements  are  reported  in  Jastrow's  Fact  and  Fable  in 
Psychology,  pp.  307-336.  One 'of  these  figures  is  repro- 
duced in  the  author's  Psychology,  General  Introduction, 
page  187. 

C — SUPPLEMENTARY   EXPERIMENTS 

The  apparatus  necessary  for  the  supplementary  experi- 
ments suggested  in  connection  with  this  exercise  is  usually 
some  form  of  tambour.     Thus,  if  a  tambour  is  pressed 
against  the  cartilages   of    the 
larynx,   a  record  will  be   se- 
cured  of   the    movements    of 
the    muscles    of    the    larynx. 
Special  frames  have  been  de- 
vised for  holding  the  tambour 
in   position  upon    the    larynx 
or    against    the    other    parts 
of  the  neck.      One  such,  de- 
vised    by    Rousselot    for    re- 
cording    upward    and   down- 
ward movements  of  the  larynx,  is  represented  in  Fig.  89. 

In  experiments  with  the  tongue,  it  is  desirable  to  pro- 
vide some  means  of  inserting  the  whole  receiving  tambour 
in  the  mouth.  For  this  purpose  rubber  bulbs  have  been 
devised  of  the  form  shown  in  Fig.  90.  These  can  be  taken 
into  the  mouth  and  can  be  held  between  the  tongue  and 
he  roof  of  the  mouth  or  between  the  tongue  and  the  teeth. 


Fio.  00 

From  Rouaaelot's  "  Principes 
Phon^tique  Experimentale  " 


172        LABORATORY  EQUIPMENT  FOR 

Such  rubber  bulbs  are  in  essence  tambours  in  which  all  of 
the  surfaces  are  more  or  less  flexible.  Any  compression  of 
the  bulb  will  drive  the  air  out  into  the  recording  tambour. 

Dynamometers  for  measuring 
the  strength  of  movements  are 
of  various  forms.  One  of  the 
simplest  forms  consists  in  a 
double  spring  and  recording 
dial  shown  in  Fig.  91.  This  is 
grasped  in  the  hand  and  pressed 
together  as  the  hand  closes. 

Instead  of  taking  merely  the 
record  of  a  single  compression, 
devices  may  be  attached  to  this  dynamometer  for  ad- 
ding up  the  movements  made  in  a  number  of  successive 
efforts;  or  instead  of  a  recording  device  directly  con- 
nected with  the  dynamometer,  a  pointer  may  be  carried 
to  a  recording  surface  and  the  amount  of  work  done  may 
be  recorded  by  tracings  on  smoked  paper. 

It  will  be  found  by  the  use  of  such  apparatus  that  the 
greater  the  stimulus  affecting  the  organs  of  sense,  the 
greater  will  be  the  amount  of  work  which  can  be  done. 

An  illusion  which  serves  very  well  to  illustrate  the  re- 
lation between  perception  and  change  in  muscular  tension 
appears  whenever  one  lifts  two  blocks  which  are  of  the 
same  objective  weight  but  are  of 
unequal  size.  Quantitative 
methods  of  determining  the 
amount  of  this  illusion  can  be 
worked  out  by  presenting  to  the 
observer  a  series  of  weights  in- 
termediate in  size  between  the  large  and  small  weight. 
The  intermediate  series  should  range  in  objective  weight 
by  short  stages  from  30%  less  than  the  weights  to  be 


Fio.  91 


PSYCHOLOGICAL  EXPERIMENTS         173 

compared  to  30%  above.  Ten  to  fifteen  weights  of  this 
sort  being  presented  to  the  observer,  he  should  be  al- 
lowed to  select  those  of  the  intermediate  weights  which 
seem  to  him  to  be  equal  to  each  of  the  two  weights  which 
constitute  the  illusion.  In  one  case,  for  example,  where 
the  primary  weights  were  55  grams,  it  was  found  that 
the  large  weight  seemed  to  the  observer  to  be  equal  to 
45  grams,  whereas  the  small  weight  seemed  to  be  equal  to 
65  grams.  The  illusion  must  therefore  be  equal  in  this 


FIG.  92 


case  to  20  grams,  which  is  somewhat  more  than  36%  of 
the  objective  weight. 

A  more  productive  method  of  dealing  with  this  illu- 
sion is  to  attach  to  each  of  the  two  weights,  levers  which 
will  record  the  way  in  which  the  observer  lifts  the  weights 
when  he  judges  of  their  intensity.  Fig.  92  shows  an  elab- 
orate apparatus  for  recording  the  movements  of  the  ob- 
server in  testing  these  weights.  A  large  weight  A  stands 
upon  a  platform  P.  By  the  side  of  A  is  a  shelf  S  upon 


174        PSYCHOLOGICAL  EXPERIMENTS 

which  is  placed  a  small  weight  B.  The  purpose  of  this 
shelf  is  to  bring  the  small  weight  B  to  the  same  level  as 
the  large  weight  A.  Each  weight  is  supplied  with  a  screw- 
eye  HHt  so  that  when  the  subject  lifts  the  weights  he  may 
have  the  same  type  of  contact  in  both  hands.  Strings 
pass  down,  as  shown  on  one  side,  from  each  of  these 
boxes  over  pulleys  YY.  These  strings  are  held  in  posi- 
tion by  weights  not  shown  in  the  figure  but  fastened  at 
the  ends  of  the  thread  at  WW.  The  threads  are  con- 
nected with  compound  levers  LL  which,  as  seen  in  the 
figure,  trace  lines  upon  the  paper,  giving  a  record  as  indi- 
cated at  R.  This  record  makes  a  comparison  between  the 
two  movements  very  easy.  When  both  boxes  are  at  rest 
the  two  levers  make  straight,  parallel  lines  as  indicated 
in  the  drawing.  When  they  are  lifted  they  describe 
curves  which  in  form  and  in  time  indicate  in  detail  the 
mode  of  lifting  the  weights.  Typical  records  from  this 
apparatus  are  described  and  discussed  by  Mr.  Loom  is  in 
the  Yale  Psychological  Studies,  New  Series,  Vol.  I,  No.  2, 
pages  334-348. 


EXERCISE  XIV 


FIG.  93 


A — APPARATUS  AND  PROCEDURE 

The  simplest  device  for  securing  a  record  of  rapid 
movements  of  the  fingers  is  a  contact  key  such  as  that 
represented  in  Fig.  93.     This  spring  key  has  a  metallic 
connection  at  the  wires  Wl  and  W2 
with  a  battery  which  supplies  a  cur- 
rent and  with  a  marker  which  records 
on  a  kymograph  whenever  a  contact 
is  made  at  the  two  points  on  P  and 
R.    The  distance  between  P  and  R 
should  be  made  as  small  as  possible 
so  that  the  electrical  contact  may  be 
made  as  soon    as  the    fingers  press 
down  upon  the  plate  R.     The  record   of  the  movement 
of  the  fingers  obtained  at  the  marker  should  be  com- 
pared with   the  standard  time-line  derived   from    some 
vibrator,  either  a  tuning-fork  or  a  vibrating  electric  rod. 

The  apparatus  for  measuring  the  rate  at  which  plain 
lines  are  drawn  by  a  reactor,  consists  in  a  wide  strip  of 
paper  which  is  drawn  forward  by  a  kymograph  under  a 
platform  upon  which  the  hand  of  the  reactor  is  supported. 
The  rate  of  the  paper  should  be  indicated  by  means  of  a 
time-line  which  is  traced  on  the  edge  of  the  paper  by  means 
of  a  pencil  or  ink  marker  such  as  that  described  on  page 
155.  If,  while  the  paper  is  moving,  the  reactor  draws  on 
the  paper  with  a  pencil  lines  perpendicular  to  the  direction 
in  which  the  paper  is  traveling,  each  line  which  is  drawn 
on  the  paper  will  be  drawn  out  into  a  record  which  is  in 

175 


176        LABORATORY  EQUIPMENT  FOR 

its  form  a  resultant  of  two  movements — the  movement 
of  the  paper,  which  is  of  known  rate,  and  the  move- 
ment of  the  hand,  which  is  to  be  measured.  A  determi- 
nation of  the  rate  of  the  hand  movement  from  this  record 
is  very  simple  so  long  as  the  hand  movement  is  strictly 
perpendicular  to  the  line  in  which  the  paper  is  traveling. 
If  the  movement  of  the  hand  is  in  some  other  direction, 
it  will  be  necessary  to  complicate  the  arrangements  thus 
far  described  by  inserting  above  the  moving  paper,  first, 
a  piece  of  carbon  paper  or  a  typewriter  ribbon,  and  second, 
a  piece  of  paper  on  which  the  line  is  to  be  drawn.  The 
paper  on  which  the  line  is  to  be  drawn,  should  in  this  case 
be  held  firmly  in  a  fixed  position.  The  moving  paper 
should  pass  beneath  the  carbon  paper  and  should  be 
marked  by  a  time  marker  to  indicate  the  rate  of  its  move- 
ment. If  now  a  line  is  drawn  freely  upon  the  upper  fixed 
paper,  a  tracing  will  be  produced  by  means  of  the  carbon 
paper  or  typewriter  ribbon  on  the  moving  paper.  The 
line  thus  traced  on  the  moving  paper  will,  as  before,  be 
the  resultant  of  the  hand  movement  and  the  rate  of  the 
movement  of  the  paper.  The  line  drawn  on  the  fixed 
paper  will  show  the  length  and  direction  of  the  hand 
movement.  Comparison  between  the  line  on  the  fixed 
paper  and  the  line  on  the  moving  paper  can  now  be  easily 
instituted,  and  the  rate  of  the  hand  movement  can  be  de- 
termined. 

An  elaborate  apparatus  constructed  on  the  principle 
just  described  is  reported  as  follows  by  Mr.  Freeman  in 
the  Yale  Psychological  Studies,  Vol.  I,  No.  2,  pages 
303-307. 

"Fig.  94  gives  a  general  view  of  the  apparatus.  Two  bars  ex- 
tending from  the  metal  base  A  support  the  roll  of  paper  and  the  spool 
of  ribbon  from  which  the  strips  B  and  F  are  unrolled.  B  and  F  pass 
across  plate  A  to  the  drum  C  and  the  spool  S,  the  latter  being  sup- 


PSYCHOLOGICAL  EXPERIMENTS         177 

ported  by  the  post  Q  and  one  not  shown  in  the  figure.  The  drum 
and  spool  are  driven  through  spur-gear  connections  by  the  shaft  G, 
which  is  in  turn  connected  with  a  driving  shaft.  The  apparatus 
is  coupled  into  the  driving  shaft  and  uncoupled  by  a  friction  clutch 


FIG.  94 

of  the  type  shown  in  Fig.  95.  This  consists  of  a  large  balance  wheel 
F  which  is  driven  by  an  electric  motor.  The  heavy  balance  wheel 
is  necessary  in  order  to  maintain  uniform  motion  when  the  appa- 
ratus is  thrown  into  gearing.  The  balance  wheel  carries  a  hollow 
cone  into  which  a  solid  cone  (W}  may  be  firmly  set  from  above.  The 
solid  cone  is  in  turn  connected  with  the  shafting  (S)  which  drives 
the  drum.  By  means  of  the  handle  (H),  which  holds  the  solid  cone 
in  a  ball-bearing  collar,  the 
solid  cone  may  be  lifted  out 
of  the  hollow  cone,  when  the 
shaft  (S)  will  be  uncoupled 
from  the  driving  wheel.  On 
the  other  hand,  when  the 
solid  cone  is  set  firmly  into 
the  hollow  cone,  the  shaft  (S) 
will  immediately  be  set  in 
operation  at  the  full  speed  of 
the  driving  wheel.  The  up- 
ward and  downward  movement  of  the  shaft  is  taken  up  by  a  slot 
device  at  the  upper  end  of  the  shaft.  By  means  of  this  clutch  the 
apparatus  shown  in  Fig.  94  can  be  set  in  motion  at  full  speed,  and 
it  can  also  be  instantly  set  free  when  the  record  is  complete. 


FIG.  95 


178         LABORATORY  EQUIPMENT  FOR 

"  In  order  to  hold  in  position  the  primary  sheet  of  paper  on  which 
the  reactor  writes  and  to  support  the  hand,  a  plate,  H,  is  placed 
over  the  primary  sheet.  A  rectangular  opening,  Nt  is  made  in  this 
plate  to  expose  a  writing  surface  on  the  primary  sheet.  The  plate, 
H,  is  hinged  at  the  back  of  the  main  base  by  two  bars,  so  that  it  may 
be  raised  to  insert  the  paper.  Fig.  96  shows  it  raised  from  the  base. 


t) 


FIG.  06 


Two  small  pins,  0,  O,  pierce  the  primary  sheet  of  paper  and  fit  in 
the  hole  Rt  and  one  not  shown  in  the  figure,  and  keep  the  primary 
sheet  from  slipping  when  the  strip  and  ribbon  pass  beneath  it.  These 
pins  are  above  and  below  the  moving  strip.  In  order  to  get  an  even 
writing  surface  the  plate  is  set  into  the  main  base,  so  as  to  lie  flush 
with  the  general  surface,  and  is  held  down  by  a  screw,  R,  Fig.  94. 
The  moving  strip  of  paper  and  ribbon  are  also  set  below  the  surface 


PSYCHOLOGICAL  EXPERIMENTS         179 

in  a  channel  which  is  cut  in  the  main  base.  Two  guides,  T,  T,  on 
each  side  of  the  moving  strip  keep  it  straight.  The  upper  ones  are 
slightly  adjustable,  so  as  to  suit  minor  differences  in  the  width  of  the 
paper. 

"  In  order  to  obtain  a  record  of  the  relative  position  of  the  primary 
sheet  and  the  moving  strip,  two  pencil  points  are  set  through  holes 
in  the  hinged  plate,  H.  These  pencil  points  make  two  dots  upon 
the  primary  sheet  and  two  lines  on  the  strip.  The  points  are  shown 
in  Fig.  94,  X,  X,  and  the  holes  through  which  they  project  in  Fig.  96, 
E,  E.  The  points  are  set  on  two  flat  springs  and  are  adjustable  with 
screws,  so  that  they  may  be  set  against  the  paper  with  varying  de- 
grees of  pressure. 

"Since  the  speed  of  movement  of  the  strip  is  not  perfectly  uniform, 
an  electric  marker  writing  tenths  of  seconds,  J,  Fig.  94,  is  pivoted 
to  a  post  set  on  the  hinged  plate,  H,  and  is  adjusted  by  a  screw  so  as 
to  bring  the  writing  point  against  the  paper.  It  writes  through  an 
opening  in  the  primary  sheet  upon  the  moving  strip  beneath.  In 
order  to  keep  the  primary  sheet  from  blotting  this  line,  it  is  held  up 
from  the  moving  strip  by  two  small  brass  clips,  T,  Fig.  96,  and  the 
time-line  passes  between  these  clips. 

"The  glass  pen,  V,  Fig.  94,  which  is  used  for  the  time  record,  is  a 
form  of  capillary  pen.  To  prevent  clogging  and  uneven  flowing, 
the  opening  in  the  point  is  made  fairly  large  and  the  flow  of  ink  con- 
trolled by  a  regulating  air  chamber.  The  upper  end  of  the  glass 
tube  is  inserted  in  a  rubber  tube  which  allows  the  point  to  move  freely, 
and  the  tube  is  connected  with  a  tambour.  The  rubber  head  of  this 
tambour  can  be  raised  or  lowered  by  a  screw,  and  the  ink  thus  made 
to  flow  slower  or  faster. 

"  Besides  the  speed  of  the  reactor's  movements,  it  is  desirable  that 
the  variations  in  the  pressure  of  the  pencil  against  the  paper  should 
also  be  recorded.  The  arrangement  for  securing  a  record  of  the 
pressure  is  shown  in  Fig.  96.  Under  the  paper  upon  which  the  re- 
actor writes  is  a  small  table  C,  set  into  an  opening  in  the  base.  The 
opening  in  which  this  table  is  set  is  situated  immediately  below  the 
opening,  N,  of  the  hinged  plate,  so  that  the  table  occupies  all  of  the 
writing  space.  The  table  is  capable  of  an  upward  and  downward 
movement,  for  it  is  fixed  to  the  two  bars,  D,  D,  which  are  in  turn 
fixed  to  the  axis  working  in  the  pivot  joints,  M,  M.  The  radius  of 
movement  of  the  table  is,  accordingly,  the  length  of  the  bars  D,  D,  or 
17  cm.,  and  the  direction  of  movement  during  a  slight  displacement 
is  practically  in  a  vertical  line,  The  extent  of  movement  of  the  table 


180        LABORATORY  EQUIPMENT  FOR 

is  magnified  five  times  by  means  of  the  lever,  F,  which  has  its  fulcrum 
at  P.  A  disk  on  the  outer  end  of  this  lever  is  in  contact  with  the 
rubber  of  the  tambour  K,  Fig.  94.  The  inner  end  of  the  lever,  which 
is  rounded,  bears  up  against  the  table,  making  a  sliding  contact.  In 
order  to  lessen  the  weight  and  consequent  inertia  of  these  parts,  the 
table  and  its  connections  are  made  of  aluminum.  The  long  arm  of 
the  lever  nearly  balances  the  weight  of  the  short  arm  together  with 
the  table  and  its  supporting  bars.  The  slight  residue  is  counter- 
balanced by  a  light  spring,  L.  This  can  be  adjusted  so  that  it  will 
bring  the  table  quickly  back  to  position,  but  will  not  prevent  a  deli- 
cate response  of  the  lever  to  a  very  light  pressure  on  the  table.  The 
spring,  L,  as  well  as  the  tambour,  with  which  a  disk  on  the  end  of  the 
lever  is  in  light  contact,  are  supported  by  a  rod,  shown  in  Fig.  94, 
fastened  to  the  main  base.  The  tambour  is  adjustable  so  that  its 
head  will  just  touch  the  lever  when  the  table  is  in  position.  This 
apparatus  responds  with  delicacy  sufficient  to  easily  record  all  the 
ordinary  changes  in  pressure  during  writing.  Tests  with  weights 
show  that  it  will  record  changes  in  pressure  of  from  20  to  300  grams. 
"The  remainder  of  the  apparatus  for  recording  pressure  is  shown 
in  Fig.  94.  The  receiving  tambour,  K,  is  connected  with  the  record- 
ing tambour  7,  which  writes  on  a  long  strip  of  smoked  paper,  E. 
This  strip  travels  over  the  drum,  D,  and  another  drum  3.5  meters 
away.  The  drum  D  is  clamped  by  an  adjustable  screw  to  the  same 
shaft  as  the  drum  C,  so  that  both  of  them  can  be  driven  together,  or 
either  one  can  be  run  separately  by  loosening  the  screw  which  clamps 
D  to  the  shaft.  Above  the  tambour  pointer  is  a  fixed  pointer  which 
traces  a  straight  line  with  which  to  compare  the  pressure  curve. 
The  pressure  curve  is  correlated  with  the  speed  curve  on  the  moving 
strip,  B,  by  means  of  one  pointer  of  the  double  marker,  L,  which  is 
in  circuit  with  the  marker  J,  on  strip  B." 

For  a  full  account  of  records  obtained  from  this  appa- 
ratus, and  methods  of  measuring  the  same,  Mr.  Freeman's 
article  should  be  consulted. 


B — RESULTS 

The  following  table  shows  in  sigmas  the  time  of  con- 
tact of  the  various  fingers  with  the  key,  and  also  the  length 


PSYCHOLOGICAL  EXPERIMENTS        181 

of  the  interval  between  each  of  the  contacts.     The  quan- 
tities in  the  table  are  averages  from  twenty-five  cases. 


Finger  I      Interval         Finger       Interval         Finger  Interval  Finger 

(Index)        after  I  II  after  II  III  after  III  IV 

Avg.  M.V.  Avg.  M.V.  Avg.  M.V.  Avg.  M.V.    Avg.  M.V.  Avg.  M.V.  Avg.  M.V. 
NATURAL  ORDER 

85   1.0    37   5.3    80   5.0    40    6.2    100  2.2  45   7.0  100   1.8 

REVERSE  ORDER 

75   1.2  116   9.8    82    1.1    89    1.5    127  3.1  51  2.3  99   2.0 


The  following  table  shows  the  average  length  of  line 
drawn  in  twenty  trials  in  successive  tenths  of  a  second. 


1st    1/10               2nd    1/10              3rd    1/10  4th    1/10  5th   1/10 

Avg.  M.V.          Avg.  M.V.          Avg.  M.V.  Avg.  M.  V.  Avg.  M.  V. 

RIGHT  HAND 

2.1    1.3       17.2    4.1       43.5    6.7  37.2    7.9  12.2    5.1 

LEFT  HAND 

1.7    1.2        11.3    6.2        31.1    7.9  36.4    8.1  9.4    3.2 


C— SUPPLEMENTARY  EXPERIMENTS 

The  experiments  here  suggested  are  referred  to  again 
in  later  exercises,  especially  in  Exercise  XIX.  The  ap- 
paratus is  not  different  from  that  required  in  general  for 
recording  movements  and  measuring  their  characteristics. 


EXERCISE  XV 

A — APPARATUS  AND  PROCEDURE. 

The  apparatus  commonly  used  for  measuring  reaction 
time  is,  first,  a  timepiece  that  will  measure  very  short  in- 
tervals of  time,  and  second,  the  accessories  which  make 
it  possible  to  measure  by  means  of  this  timepiece  the  in- 
terval which  elapses  between  the  signal  to  react  and  the 
reaction  movements. 

The  simplest  arrangement  for  measuring  reactions  re- 
quires no  other  apparatus  than  that  which  has  already 
been  described.  Let  a  contact  key,  such  as  that  used  in 
Exercise  XIV,  be  connected  with  an  electric  marker  which 
records  on  a  kymograph.  The  marker  should  be  allowed 
to  trace  in  parallel  with  the  record  of  a  tuning-fork.  In 
this  case  the  tuning-fork  record  should  be  made  if  possible 
from  a  fork  vibrating  at  the  rate  of  500  times  a  second. 
Another  marker  should  be  introduced  to  record  the  mo- 
ment at  which  the  stimulation  for  the  reaction  is  given  to 
the  reactor.  This  marker  should  be  connected  with  a 
second  key,  which  makes  a  sound  that  serves  as  the  signal 
to  react  and  at  the  same  time  completes  the  electric  cir- 
cuit passing  through  the  marker.  With  these  three 
records — that  of  the  reaction  key,  that  made  by  the  tuning- 
fork,  and  that  made  by  the  apparatus  which  gives  the  signal 
for  reaction — it  is  possible  to  determine  the  number  of 
tuning-fork  vibrations  which  lie  between  stimulus  and 
reaction.  Such  determinations  as  would  be  possible  with 
the  arrangement  just  described  involve  a  great  deal  of 
counting  of  tuning-fork  vibrations;  consequently,  other 

182 


PSYCHOLOGICAL  EXPERIMENTS        183 

forms  of  apparatus  have  been  devised  and  are  in  common 
use,  which  obviate  the  necessity  of  such  elaborate  counting. 
A  simple  and  very  convenient  form  of  chronoscope 
which  can  be  used  in  connection  with  a  tuning-fork  to 
obviate  counting  is  the  Ewald  Chronoscope,  which  is  rep- 
resented diagrammatically  in  Fig.  97.  Its  essential  parts 
are  a  pair  of  small  electromagnets  M  which  can  be  put  in 
the  circuit  of  an  electric  current  which  is  made  and  broken 
by  a  100-vibration  fork. 
This  pair  of  electromag- 
nets, being  supplied  with 
an  electric  current  every 
1-100  of  a  second,  can 
be  made  to  set  in  oscilla- 
tion a  little  plate  P  which 
hangs  in  front  of  the 
magnets  and  is  drawn 
away  from  them  by  the 
spring  S  whenever  the 
current  is  broken.  The 
plate  thus  set  in  vibration 
is  connected  by  means  of 
a  short  rod  with  a  fine 
toothed  wheel  which  has 
the  form  of  an  ordinary 

clock-work  ratchet.  Each  time  the  rod  is  thrown  for- 
ward into  this  wheel  it  advances  the  wheel  one  tooth, 
so  that  the  rate  of  the  movement  of  the  wheel  will  be 
one  tooth  in  every  1-100  of  a  second.  Connected  with 
the  ratchet  wheel  is  a  hand  T,  which  moves  across  the 
face  of  a  circular  dial,  graduated  so  that  one  graduation  is 
equal  to  each  tooth  of  the  ratchet  wheel .  If  no w  the  electric 
current  from  the  tuning-fork  is  allowed  to  pass  through  the 
electromagnets  for  any  length  of  time,  the  hand  on  the  dial 


FIG.  97 


184        LABORATORY  EQUIPMENT  FOR 

of  the  chronoscope  will  travel  over  a  number  of  gradua- 
tions equal  to  the  number  of  vibrations  of  the  fork  which 
occur  between  the  beginning  and  the  end  of  the  introduc- 
tion of  the  current  into  the  electromagnets.  In  order  to 
measure  reaction  times,  connections  should  be  provided 
such  that  the  current  from  the  fork  will  begin  to  pass 
through  the  electromagnets  at  the  instant  that  the  signal 
for  the  reaction  is  given,  and  will  cease  to  pass  through 
the  electromagnets  the  instant  that  the  reactor  moves  his 
hand.  The  proper  connections  are  indicated  in  Fig.  98. 
The  current  from  the  battery  B  passes  at  F  through  the 
fork  and  at  K  through  a  key.  This  key  is  a  break  key; 


FIG.  98 

that  is,  when  in  position,  the  current  passes  through  it, 
when  the  experimenter  presses  down  on  it  the  current  is 
interrupted.  From  the  points  /  and  Z,  at  which  the  wires 
from  the  battery  and  fork  connect  with  the  key  K,  a  second 
circuit  leads  through  the  Ewald  Chronoscope  (7,  and  a 
second  key  M.  The  key  M  is  the  reactor's  key  and  at  the 
beginning  of  the  experiment  is  closed.  This  second  cir- 
cuit supplies  the  path  for  the  current  when  the  contact  at 
K  is  broken.  If  the  circuit  is  broken  by  taking  the  finger 
off  the  key  M,  as  it  is  when  the  reactor  raises  his  hand, 
the  current  will  no  longer  pass  through  the  chronoscope. 
A  reaction  time  experiment  in  its  simplest  form  can  be 


PSYCHOLOGICAL  EXPERIMENTS 


185 


carried  out  with  this  apparatus  by  requiring  the  reactor 
to  prepare  for  the  experiment  by  pressing  down  upon  the 
key  M.  The  making  of  this  contact  without  a  breaking 


FIG.  99 

From  Wundt's  "Grundziige  der  physiologischen  Psychologie  " 
5th  Ed.,  Vol.  Ill,  p.  339 

of  the  current  at  K  is  not  sufficient  to  drive  the  current 
through  the  Ewald  Chronoscope,  because  of  its  relatively 
high  resistance.  The  reactor  may,  accordingly,  make 
preparation  in  this  way  for  the  experiment  without  starting 


186         LABORATORY  EQUIPMENT  FOR 

the  chronoscope.  The  signal  to  react  is  given  by  the  ex- 
perimenter by  striking  the  key  K.  The  simplest  signal  for 
reaction  is  the  sound  thus  produced  at  the  key  K.  The 
Ewald  Chronoscope  will  be  set  in  motion  by  the  current 
coming  from  the  electric  tuning-fork  at  the  instant  that 


Fio.  100 

From  Wundt's  "Grundziige  der  physiologischen  Psychologic," 
5th  Ed..  Vol.  Ill,  p.  392 

K  is  depressed,  and  it  will  continue  in  operation  until  the 
hand  of  the  reactor  is  lifted  from  the  key  M.     The  number 
of  1-100's  of  a  second  that  the  chronoscope  was  in  operation 
can  now  be  read  on  the  scale  and  this  is  the  reaction  time. 
A  more  elaborate  chronoscope  is  that  which  is  known 


PSYCHOLOGICAL  EXPERIMENTS        187 

as  the  Hipp  Chronoscope.  This  chronoscope  consists  of 
three  essential  parts.  First,  there  is  a  clock-work  which 
is  represented  in  outline  in  Fig.  99.  Instead  of  being 
controlled  by  a  pendulum  as  is  an  ordinary  clock,  the  works 
of  the  Hipp  Chronoscope  are  controlled  in  their  rate  by 
the  vibration  of  a  fine  metallic  rod,  F,  Fig.  99.  This  rod 
vibrates  at  the  rate  of  250  times  per  second,  and  releases 
the  clock-work  at  a  high  rate  of  speed,  and  at  the  same  time 
regulates  that  speed  so  that  the  clock-work  moves  uniformly 
under  its  control.  The  same  works  which  are  seen  from 
in  front  in  Fig.  99,  are  shown  from  the  side  in  the  middle 
section  of  Fig.  100.  The  clock-work  drives  the  toothed 
wheel  K1  (Fig.  100)  but  not  the  similar  wheel  K2. 

The  recording  pointer  and  dial  constitute  the  second 
part  of  the  chronoscope.  The  dial  is  made  up  of  two  scales, 
the  upper  one  of  which  indicates  when  the  pointer  moves 
over  a  single  graduation  one  one-thousandth  of  a  second, 
or  a  sigma  as  it  is  called.  The  lower  dial  and  pointer 
which  are  connected  with  the  upper  by  proper  reducing 
gears,  record  tenths  of  a  second.  When  the  shaft  of  the 
recording  parts  is  thrown  into  the  clock-work  so  as  to 
move  at  the  same  rate  as  the  clock-work,  as  it  is  when  the 
stylus  h  is  held  in  the  wheel  Klf  the  period  of  time  that 
elapses  between  the  beginning  of  the  movement  of  the  re- 
cording apparatus  and  the  end  of  that  movement  can  be 
read  on  the  dial. 

The  third  part  of  the  Hipp  Chronoscope  consists  of  a 
pair  of  electromagnets  Elt  E2  (Fig.  100)  which  make  it 
possible  to  control  the  reading  part  of  the  apparatus  so 
that  it  will  move  with  the  clock-work  or  come  to  a  stand- 
still. Between  the  electromagnets  is  placed  a  metallic 
plate  ra,  which  is  also  controlled  in  some  cases  by  means  of 
springs  not  shown  in  the  figure.  This  metallic  plate  can 
be  drawn  up  or  down  by  the  magnets,  according  as  the  one 


188        LABORATORY  EQUIPMENT  FOR 

or  the  other  carries  an  electric  current.  Whenever  TO 
moves  downward  it  acts  through  H 3  so  as  to  throw  h  into 
the  wheel  Kv  When  m  moves  upward  it  throws  h  into 
the  wheel  K2  and  prevents  the  hands  of  the  dials  from 
moving.  The  accessory  connections  are  very  similar  to 
those  shown  in  Fig.  98,  and  are  shown  in  full  in  Fig.  101. 
Two  keys,  KR  and  KE  are  placed  in  circuit  with  the  lower 
magnet  of  the  chronoscope.  For  the  sake  of  simplicity  let 
it  be  assumed  that  the  plate  m  is  in  this  case  held  away 
from  the  lower  magnet  by  a  spring.  If  now  either  key 
is  opened  no  current  will  pass  through  the  chronoscope. 
The  clock-work  may  be  set  in  motion  without  carrying 
the  recording  arms  on  the  dials  with  it.  Preparation  for 


Fio.  101. 


the  experiment  may  be  made  by  requiring  the  reactor  to 
press  down  the  key  KR.  By  pressing  down  upon  this 
key,  the  reactor  closes  one  of  the  breaks  in  the  electric 
circuit,  but  there  will  still  be  a  break  at  the  key  KE,  and 
the  current  will,  therefore,  not  pass  through  the  electro- 
magnet in  the  chronoscope.  After  the  reactor  has  pre- 
pared for  the  experiment  by  closing  the  circuit  at  KR,  the 
experimenter  may  start  the  clock  face  by  pressing  upon 
key  KE.  This  pressure  upon  key  KE  allows  the  current 
from  the  battery  B  to  pass  through  the  electromagnets  in 
the  chronoscope  (L)  and  sets  the  recording  arms  on  the 
dial  in  operation.  The  movement  of  the  recording  face 
will  continue  until  the  reactor  again  breaks  the  circuit  by 


PSYCHOLOGICAL  EXPERIMENTS         189 

lifting  his  finger  from  KR.  The  reading  on  the  dial  will, 
therefore,  correspond  exactly  to  the  interval  that  elapses 
between  the  pressure  upon  KE  and  the  breaking  of  the  cir- 
cuit at  KR.  X  is  a  commutator  which  changes  the  di- 
rection of  the  current  after  each  reaction. 

The  experiment  may  be  made  more  elaborate  by  intro- 
ducing other  pieces  of  apparatus  into  the  circuit.  Thus, 
instead  of  allowing  KE  to  close  the  circuit  through  the  clock, 
the  experimenter  may  arrange  a  secondary  circuit  whereby 
his  pressure  upon  KE  will  cause  an  electric  hammer  to  sound. 
The  electric  hammer-head  can  be  made  to  close  the  circuit 
through  the  clock,  other  connections  remaining  the  same 


FIG.  102 
From  the  catalogue  of  Zimmermann,  Leipzig,  Germany 

as  in  the  first  case  described.  Fig.  102  represents  an  elec- 
tric sound  hammer.  The  sound  hammer  consists  of  a 
long  handle  P  and  a  metallic  hammer-head  H.  An  elec- 
tromagnet E  is  so  placed  that  it  may  draw  the  rod  P  down- 
ward and  thus  cause  a  sound  by  the  forcible  contact  of 
H  upon  the  metal  plate  under  it.  Electric  connections 
for  sounding  the  hammer  are  made  through  the  magnet. 
The  necessary  contacts  for  starting  the  clock  may  be  made 
by  connecting  one  wire  with  H  through  the  rod  P  and  a 
second  wire  with  the  plate  upon  which  H  strikes.  The 
current  will  now  pass  through  the  two  wires  when  H  and 
the  plate  under  it  are  in  direct  contact.  A  convenient 


190        LABORATORY  EQUIPMENT  FOR 

substitute  for  a  sound  hammer  is  the  common  telegraph 
sounder.  This  is  essentially  a  sound  hammer  in  princi- 
ple and  has  adjustments  for  controlling  the  extent  of  the 
movement  and  the  consequent  intensity  of  the  sound. 

In  practical  use  the  Hipp  Chronoscope  requires  very 
careful  handling.  In  the  first  place,  care  must  be  taken 
to  keep  the  magnets  from  becoming  permanently  magne- 
tized. If  the  current  is  allowed  to  pass  through  the  mag- 
nets in  the  same  direction  a  number  of  times  in  succession 


Fio.  103 
From  the  catalogue  of  Zimmermann,  Leipzig,  Germany 

there  is  danger  that  they  will  gradually  become  so  strong 
that  the  release  under  the  tension  of  the  spring  when  the 
current  is  broken  will  be  slow,  and  an  error  will  thus  be  in- 
troduced into  the  readings  of  the  chronoscope.  For  this 
reason  the  current  should  be  changed  in  direction  each 
time  it  is  sent  through  the  electromagnets  of  the  chrono- 
scope. This  can  be  readily  done  by  means  of  a  simple 
mercury  commutator. 

In  the  second  place,  the  relation  between  the  strength 
of  the  current  and  the  tension  of  the  springs  should  be  so 


PSYCHOLOGICAL  EXPERIMENTS        191 

adjusted  that  the  chronoscope  acts  uniformly.  The  best 
method  of  establishing  and  maintaining  this  relation  is  to 
adjust  and  test  the  chronoscope  by  comparing  it  with  a 
mechanical  device  which  will  operate  the  clock  during 
the  time  which  elapses  between  the  beginning  and  the  end 
of  the  movement  of  a  heavy  falling  body.  One  of  the 
most  common  forms  of  control  apparatus  is  the  control 
hammer,  represented  in  Fig.  103.  This  makes  and  breaks 
two  electric  contacts  at  A  and  B  in  the  course  of  its  fall. 
The  hammer  H  is  held  in  position  by  the  magnet  M  until 
the  clock  is  started,  when  it  is  released.  As  O  passes  A  in 
the  descent  of  the  hammer  the  clock  is  started.  When 
H  strikes  B  the  clock  is  stopped.  The  chronoscope  should 
not  vary  in  successive  trials  with  such  a  mechanical  de- 
vice, if  it  does  it  needs  readjustment.  Other  forms  of 
control  apparatus  may  be  made  to  operate  contacts, 
or  a  freely  falling  body  may  be  used. 

There  are  a  number  of  pendulum  chronoscopes  which 
have  been  devised  as  substitutes  for  the  various  clocks 
and  electrical  apparatus  described.  The  range  of  use- 
fulness of  these  pendulum  chronoscopes  is  by  no  means 
as  large  as  that  of  the  various  types  of  apparatus  des- 
cribed. Reference  may  be  made,  if  one  desires  to  be- 
come familiar  with  this  type  of  apparatus,  to  descrip- 
tions by  Professor  Scripture  in  his  New  Psychology, 
Chapter  IX,  page  155,  and  Professor  Sanford  in  the 
American  Journal  of  Psychology,  Vol.  XII  (1901),  pp. 
590-594. 

The  procedure  in  reaction  experiments  is  complicated 
by  the  necessity  of  securing  the  maximum  attention  of  the 
reactor  just  before  the  signal  is  given.  It  has  been  found 
advantageous  to  warn  him  two  seconds  before  the  stimulus 
in  order  that  he  may  be  fully  prepared.  If  the  warning 
is  given  less  than  two  seconds  in  advance,  the  period  of 


192        LABORATORY  EQUIPMENT  FOR 

preparation  has  been  found  to  be  in  general  inadequate. 
If  it  is  given  more  than  two  seconds  in  advance,  attention 
flags  before  the  arrival  of  the  signal  to  react. 

It  is  advantageous,  where  this  is  possible,  to  remove 
the  reactor  far  enough  from  the  apparatus  so  that  he  will 
not  be  distracted  by  preparations. 

In  all  of  the  earlier  investigations  of  reactions  the  equip- 
ment which  has  been  described  up  to  this  point  was  re- 
garded as  entirely  adequate.  It  was  assumed  that  the 
hand  reaction  under  the  simple  conditions  presented  was 
uniform.  It  has  been  made  very  clear  by  recent  investi- 
gations that  this  is  not  the  case,  and  that  there  is  much 
productive  information  to  be  gained  from  an  examina- 
tion of  the  form  of  hand  movement  involved  in  simple  re- 
actions. In  the  simplest  case  this  investigation  of  the 
form  of  movement  may  be  altogether  dissociated  from  the 
measurements  of  duration.  The  finger  of  a  reactor  may 
be  placed  on  a  receiving  tambour  or  on  a  lever  which  is  so 
placed  that  it  records  directly  on  a  kymograph,  and  the 
reactor  may  be  required  to  react  to  a  signal.  If  the  record 
thus  secured  is  accompanied  by  a  standard  time-line,  the 
time  of  the  various  phases  of  the  movement  may  be 
measured  by  counting  the  vibrations  in  the  time-line. 

If  an  electrically  controlled  chronoscope  is  at  hand,  a 
graphic  record  may  be  taken  from  a  tambour,  and  at  the 
same  time  the  chronoscope  may  be  used  to  measure  the 
reaction  time.  In  this  case  the  tambour  should  be  sup- 
plied with  a  metal  sheet  and  the  reactor  should  have  a 
metallic  cap  fixed  to  his  finger.  Fine  wires  should  be  led 
from  the  metal  plate  of  the  tambour  and  finger  cap  to  the 
chronoscope  and  the  battery  that  supplies  the  current 
for  the  chronoscope  magnet,  just  as  in  Fig.  101  connec- 
tions passed  through  the  clock  from  the  reactor's  key,  KR. 
The  reactor  should  bring  the  two  metal  plates  into  contact 


PSYCHOLOGICAL  EXPERIMENTS         19S 

in  such  a  way  as  to  depress  the  rubber  of  the  tambour. 
If  this  tambour  is  connected  with  a  recording  tambour, 
any  change  in  the  pressure  of  the  finger  will  be  recorded 
by  the  recording  tambour.  The  reaction  from  this  ap- 
paratus will  proceed  exactly  as  in  the  earlier  cases  by  the 
lifting  of  the  reactor's  finger.  Some  care  must  be  exer- 
cised to  make  the  tambour  sufficiently  large  so  that  the 
rate  of  movement  of  the  rubber  surface  in  its  recovery  will 
not  be  equal  to,  or  greater  than,  the  rate  of  the  finger  as  it 
is  raised  in  reaction.  If  the  movement  of  the  rubber  is 
equal  to,  or  greater  than,  that  of  the  finger,  the  plates  of 


FIG.  104 

the  tambour  and  finger  cap  will  be  kept  in  contact  even 
after  the  reactor  begins  to  raise  the  finger.  The  reaction 
time  will,  by  this  purely  mechanical  process  be  somewhat 
exaggerated  in  length.  This  difficulty  may  be  overcome 
by  making  the  rubber  face  of  the  tambour  relatively  large, 
when  the  rate  of  its  movement  will  be  slow. 

An  especially  devised  apparatus,  which  gives  great 
range  to  this  type  of  experiment,  is  shown  in  Fig.  104. 
On  a  heavy  table  H  is  erected  a  firm  post  G.  This  post 
should  be  about  15  cm.  high  and  has  screwed  into  its  top 
a  long  strip  of  spring  brass  seen  from  the  side  in  the  figure 
at  A.  This  strip  of  spring  brass  is  25  cm.  long  and  5  cm. 


194        LABORATORY  EQUIPMENT  FOR 

wide.  The  spring  when  in  use  is  depressed  with  its  at- 
tached parts  to  the  position  indicated  by  the  dotted  lines. 
The  dimension  of  the  spring  may  be  determined  empiri- 
cally. It  must  be  made  of  such  size  that  its  rate  of  oscilla- 
tion, when  set  free  from  its  depressed  position,  is  slower 
than  the  rate  at  which  the  hand  or  finger  of  a  reactor  is 
lifted  in  making  a  rapid  reaction  movement.  The  method 
of  determining  the  proper  rate  of  the  spring  is  very  simple. 
Several  reactors  are  required  to  record  on  a  kymograph 
by  means  of  a  simple  lever  the  rate  of  their  movements 
when  lifting  the  hand  as  they  would  in  an  ordinary  reac- 
tion. The  spring  is  then  made  enough  slower  than  the 
slowest  of  these  hand  movements  to  insure  its  rising  more 
slowly  than  the  hand  of  any  reactor.  The  rate  of  the 
spring  is,  on  the  other  hand,  fast  enough  so  that  any 
gradual  movement  of  the  hand  upward  will  not  separate 
the  finger  and  spring.  Put  in  other  terms,  the  spring  will 
follow  faithfully  any  slow  upward  movements  of  the  hand, 
and  it  can,  of  course,  be  pressed  downward  by  any  down- 
ward movement  of  any  rate  whatsoever. 

At  the  end  of  the  spring  A  there  is  attached  at  a  ful- 
crum C  the  reaction  key  M.  This  key  is  closed  by  press- 
ing downward  at  M .  The  contacts  n  n,  n'n'  are  brought 
together  by  such  a  downward  pressure.  There  is  a  small 
spring  at  B  against  which  the  downward  pressure  applied 
by  the  finger  at  M  is  exerted.  This  small  spring  B  tends 
to  separate  the  contacts  n  n,  n'n'.  If  A  were  a  rigid  rod 
instead  of  a  spring,  the  small  spring  B  would  be  brought 
into  action  at  the  slightest  movement  of  the  finger  upward 
from  M.  But  since  A  is  a  heavy  slow  spring  and  B  is  a 
small  rapid  spring,  we  have  the  following  complex  results  of 
finger  movements  at  M.  When  the  finger  is  pressed 
downward  at  M  it  overcomes  the  spring  B  and  brings  to- 
gether the  contact  n  n,  n'n'.  At  the  same  time  it  flexes  the 


PSYCHOLOGICAL  EXPERIMENTS 

spring  A  for  a  short  distance.     As  soon  as  n  n,  n' 
firmly  closed,  any  further  downward  pressure  will 
pended  altogether  in  the  flexion  of  A.     In  practical  use 
the  spring  A  is  flexed  for  some  distance  after  the  contact  \ 
are  firmly  closed.     This  flexion  of  A  beyond  the  point  oi' 
closing  the  contacts  may  be  described   as  the  surplus 
flexion  of  A. 

If  now  the  finger  rises  at  a  rate  which  is  slower  than 
that  at  which  the  large  spring  A  would  naturally  recover 
its  position  of  rest,  the  contacts  n  n,  n'n'  will  remain 
closed  through  the  whole  of  what  has  been  called  the  sur- 
plus flexion  of  A.  If  the  finger  is  pressed  downward  at 
any  rate  whatsoever,  the  contacts  will  remain  closed. 
There  is  one  case  of  movement  in  which  the  contact  will 
be  immediately  broken.  That  is  the  case  of  a  rapid  re- 
action movement  upward.  If  the  movement  upward  is 
more  rapid  than  the  rate  of  the  spring  A,  as  it  is  for  ex- 
ample in  a  reaction  movement  of  the  ordinary  type, 
then  the  lifting  of  the  finger  from  M  will  immediately  call 
into  play  the  small  rapid  spring  B,  and  n  n,  n'n'  will  be 
separated  by  B  without  reference  to  the  slow  upward 
movement  of  A. 

This  combination  of  springs  gives  us  all  the  conditions 
necessary  for  maintaining  a  contact  at  n  n,  n'n'  until  the 
reaction  takes  place,  while  it  leaves  the  hand  free  to  move 
downward  at  any  rate  whatsoever,  or  to  move  upward 
at  any  rate  slower  than  that  of  the  spring  A. 

The  method  of  recording  any  upward  or  downward 
movements  of  the  reacting  hand  is  to  attach  a  long  lever 
to  the  post  G  at  0,  and  place  one  end  in  contact  with  the 
key  M  while  the  other  end  traces  on  a  kymograph  at  E. 
This  connection  may  be  of  the  form  shown  in  the  figure 
or  it  may  consist  in  some  other  form  of  lever  connection. 
A  marker  may  be  attached  to  the  lever  as  at  F  and 


196        LABORATORY  EQUIPMENT  FOR 

may  record  the  signal  to  react  and,  if  desired,  the  reaction 
itself. 

rf  The  extent  of  the  hand  movement  to  be  recorded  and 
'0.  e  necessity  of  trying  long  series  of  experiments  in  rapid 
1  accession  make  it  convenient  to  use  on  the  kymograph 
che  long  belts  of  paper  described  under  Exercise  XL  The 
adjustment  of  a  belt  running  in  the  vertical  differs  from 
the  adjustment  of  a  horizontal  belt  somewhat,  but  will  be 
easily  mastered  by  one  who  has  learned  to  adjust  horizontal 
belts. 

B — RESULTS 

Table  of  reactions  expressed  in  one-hundredths  of  a 
second. 


Reactor 

Sensory 

No.  of  deter- 
minations 

Motor 

No.  of  deter- 
minations 

A 
B 
C 

Avg.      M.V. 

Avg.    M.V. 

19.5        4.3 
15.5        1.5 
22.6        5.9 

10 
10 
10 

17.4      1.7 
15.0      2.0 
14.3      5.0 

10 

10 
10 

For  complete  statement  as  to  forms  of  reaction,  see 
Yale  Psychological  Sludies,  New  Series,  Vol.  I,  pages 
141-184. 

C — SUPPLEMENTARY   EXPERIMENTS 

If  the  reaction  is  to  be  to  visual  stimuli  a  very  simple 
exposure  apparatus  may  be  set  up  as  follows.  Connect 
with  the  key  which  is  to  make  the  contact  a  long  lever. 
Let  the  end  of  this  lever  be  hidden  from  the  reactor  behind 
a  screen  when  the  key  is  not  in  use.  Behind  this  screen 
various  colors,  letters,  or  other  visual  stimuli  may  be 
attached  to  the  lever.  The  screen  should  be  of  such  a 
size  that  when  the  key  is  closed  the  end  of  the  lever 


PSYCHOLOGICAL  EXPERIMENTS         197 

with  its  attached  visual  object  will  appear  through  an 
opening  in  the  screen,  and  this  become  visible  to  the 
reactor.  A  simple  form  of  shutter  on  this  principle  is 
shown  in  Fig.  105.  In  this  figure  the  opening  in  the 
screen  and  the  key  are  shown.  The  reactor  is  placed  on 
the  opposite  side  of  the  screen. 

A  simple  visual  exposure  apparatus  consists  of  a  board 
which  can  fall  between  two  guides  and  which  has  in 
its  center  a  hole  through  which  a  series  of  letters  or 
figures  can  be  exposed.  In  its  first  position  the  board 
covers  these  letters,  in  its  last  it  exposes  them  to  view  and 


FIG.  105 

at  the  same  time  by  means  of  metallic  strips  at  the  side 
makes  any  desired  electric  contacts. 

The  disadvantages  with  the  fall  apparatus  and  also 
with  the  simple  shutter  shown  above  are:  first,  both 
pieces  produce  a  sound  as  well  as  expose  letters  to  view; 
and,  furthermore,  since  there  is  a  general  movement  of 
the  whole  field  during  the  exposure  there  is  large  probabil- 
ity that  the  observer  will  be  distracted  by  the  general 
movement  in  the  field.  An  ideal  visual  exposure  apparatus 
is  one  which  presents  the  visual  object  to  view  without 
any  apparent  motion  in  the  field.  In  order  to  obtain  these 
ideal  conditions  the  light  which  falls  upon  the  visual  field 


198        LABORATORY  EQUIPMENT  FOR 

should  be  cut  off  and  turned  on,  rather  than  the  field  itself 
either  moved  or  exposed  by  a  falling  shutter. 

It  is  very  easy  to  control  the  light  which  is  to  fall  upon 
a  given  visual  field  provided  this  light  is  brought  to  a  focus 
as  indicated  in  Fig.  106  A.  By  means  of  the  small  bright 
light  L,  the  lenses  /  and  A7,  and  the  diaphragms  S1,  S2, 
and  «S3,  the  field  O  is  easily  illuminated  or  darkened  by 
a  shutter  placed  at  H.  The  visual  field  0  is  enclosed  in 
a  dark  box  and  is  so  placed  that  when  the  rays  of  light  are 
cut  off  by  the  shutter  H  the  field  is  entirely  invisible  be- 


N        M 


00 


Fio.  106 


cause  it  stands  in  the  dark.  When  the  shutter  opens, 
the  field  is  exposed  and  its  whole  area  will  be  visible  at 
the  same  time.  There  will  be  no  movement  anywhere 
visible  in  the  field.  The  exposure  shutter  may  in  this  case 
be  of  a  very  simple  type,  consisting  of  a  metallic  wheel 
shown  in  detail  in  Fig.  106  B.  At  its  outer  part  this  disk 
is  made  adjustable  so  that  openings  of  different  sizes  may 
be  made  at  T.  The  shutter  is  made  to  rotate  by  attaching 
a  weight  W  to  its  axis.  The  shutter  is  stopped  by  means 
of  a  brake,  which  consists  of  a  wedge  (R)  attached  to  the 
shutter  and  a  felt  pad  D  which  is  held  in  position  by  a 


PSYCHOLOGICAL  EXPERIMENTS        199 

spring  not  shown  in  the  figure.  This  break  holds  the 
shutter  firmly  in  position  after  it  has  exposed  the  visual 
field. 

.Fig.  107  shows  a  key  designed  by  Professor  Scripture 
to  give  tactual  stimulations.  A  heavy  rod  H  is  set  into 
a  handle  and  is  connected  with  a  wire.  The  flexible  rod 
N  is  placed  above  H  and  in  electrical  contact  with  it. 
At  the  end  of  N  is  a  small  hard  rubber  point  with  which 
pressure  is  to  be  exerted  on  the  skin.  When  this  point 
is  brought  against  the  skin,  it  breaks  the  contact  between 
N  and  H. 

It  is  frequently  desirable  to  make  a  number  of  different 
contacts  simultaneously  in  order  to  set  different  pieces  of 


FIG.  107 
From  the  "  Studies  from  the  Yale  Psychological  Laboratory,"  Vol.  III. 

apparatus  in  action  at  the  same  instant.  A  very  good 
means  of  securing  simultaneous  contact  has  been  devised 
by  Professor  Angell.  It  consists  of  a  large  wooden  cyl- 
inder upon  which  are  fastened  at  certain  points  metallic 
strips  which  extend  over  only  a  part  of  the  circumference 
of  the  cylinder.  Adjustable  brushes  are  set  against  the 
surface  of  this  cylinder.  When  in  contact  with  the  wooden 
cylinder  these  brushes  make  no  electric  contact.  If  now 
the  cylinder  is  turned  until  the  brushes  come  in  contact 
with  the  metallic  strips  referred  to  above  as  fastened  to 
the  surface  of  the  cylinder,  a  contact  will  be  made  between 
each  brush  and  the  metallic  strip  with  which  it  comes  into 
contact.  By  carefully  adjusting  the  brushes  so  that  two 


200        PSYCHOLOGICAL  EXPERIMENTS 

or  three  come  into  contact  with  their  respective  metallic 
strips  at  the  same  moment,  a  series  of  contacts  can  be 
made  simultaneously.  The  advantage  of  the  large  cyl- 
inder is  that  the  contacts  can  be  adjusted  to  secure  abso- 
lute precision  in  the  making  or  breaking  of  the  contacts. 

The  supplementary  experiments  which  require  records 
of  hand  movements  are  closely  related  to  the  experiments 
required  in  Exercise  XVII.  The  apparatus  there  described 
in  full  may  be  used  for  these  experiments. 


EXERCISE  XVI 


A — APPARATUS   AND   PROCEDURE 


Most  of  the  apparatus  necessary  for  this  exercise  has 
been  described.  For  choice  reactions  the  colors  or  sounds 
may  be  produced  by  means  of  one  of  the  exposure  screens 
or  by  means  of  two  or  more  hammers  placed  in  various 


FIG.  108 

From  Wundt's  "  Grundziige  der  physiologischen  Psychologie," 
5th  Ed.,  Vol.  Ill,  p.  403 

positions.  Reaction  keys  for  more  than  one  ringer  can 
be  constructed  by  bringing  together  in  compact  form  a 
series  of  finger  pieces  which  control  electric  contacts. 

For  recording  the  reactions  of  articulation  the  simplest 
device  is  to  require  the  reactor  to  move  his  hand  at  the 

201 


202        LABORATORY  EQUIPMENT  FOR 

same  time  that  he  utters  the  word.  This  method  is  not 
satisfactory  because  some  error  arises  when  the  reactor 
attempts  to  make  two  simultaneous  movements.  The 
only  satisfactory  method  is  to  secure  a  record  from  the 
articulation  movement  itself.  For  this  purpose  a  special 
voice  key  may  be  used.  The  most  satisfactory  form  of 
voice  key  is  represented  in  Fig.  108.  A  large  mica  plate 
is  placed  at  the  end  of  a  funnel.  The  mouth  is  placed 
against  the  opening  of  this  funnel  M  and  a  word  is  sounded 
into  the  air  chamber.  The  vibrations,  as  well  as  the  change 
in  the  pressure  of  the  air,  set  the  mica  plate  in  oscillation. 
On  the  surface  of  this  mica  plate  is  a  small  platinum  con- 
tact C.  An  adjustable  point  controlled  by  means  of  the 
screw  is  set  so  that  it  is  in  contact  with  the  platinum  at- 
tached to  the  mica  plate.  Wires  pass  from  the  two  poles 
of  this  contact.  These  two  wires,  instead  of  being  con- 
nected directly  with  the  chronoscope,  are  first  carried  to  a 
relay  apparatus.  The  relay  is  a  piece  of  apparatus  which 
may  be  set  so  that  when  it  is  once  released  by  means  of  an 
instantaneous  electric  current,  it  will  not  return  to  its 
original  position  unless  it  is  deliberately  set  in  position. 
A  simple  form  of  relay  is  represented  in  Fig.  108  at 
the  right.  A  metallic  strip  T  is  connected  with  the  spring 
F  which  tends  to  draw  it  away  from  the  electro-mag- 
nets. When  the  apparatus  is  set  ready  for  use,  the 
metallic  strip  T  is  held  in  position  by  the  magnets  which 
are  supplied  with  a  current  through  the  mouth-key  de- 
scribed above.  If  now  the  current  is  broken  even  an  in- 
stant by  vibrations  in  the  voice  key,  the  metallic  strip  T 
is  released  by  the  magnets  and  responds  to  the  tension  of 
the  spring  F.  When  once  it  is.  drawn  away  from  the 
magnets  it  does  not  return  with  the  reestablishment  of 
the  current  in  the  magnets.  At  the  lower  end  of  T  are 
electric  contacts  which  are  broken  or  made  with  the  move- 


PSYCHOLOGICAL  EXPERIMENTS        203 

merits  of  the  strip.  In  this  way  an  intermittent  make  and 
break,  such  as  that  which  results  from  the  vibration  of  the 
voice  key  above  described,  is  converted  into  a  permanent 
break  the  moment  the  current  in  the  voice  key  is  inter- 
rupted. From  this  point  the  connections  from  the  chrono- 
scope  are  as  from  the  regular  break  key  and  require  no 
special  description. 

B — RESULTS 

The  following  discrimination  times  are  reported  for 
reactor  B,  for  whom  simple  reaction  times  were  reported 
on  page  196.  These  times  are  long.  They  are  expressed 
in  one-hundredths  of  a  second. 

Avg.         M.V. 

10  Discriminations  of  Green  and  Yellow 44.7        3.6 

10  Discriminations  of  Red  and  Blue . .52.8      13.8 

Articulation  times  from  reactors  who  pronounced 
printed  words  exposed  to  view  are  given  in  sigmas  as  fol- 
lows: Train,  560;  boat,  570;  blot,  440;  tank,  1100;  dark, 
540. 

Association  times  for  free  associations  are  as  follows: 
Boat — water,  980;  train — smoke,  850;  bank — money,  1270. 

C — SUPPLEMENTARY   EXPERIMENTS 

A  very  good  discrimination  experiment  consists  in  pre- 
senting to  the  reactor  a  number  of  different  pairs  of  colors 
which  differ  qualitatively  from  each  other  in  various  de- 
grees. Thus,  one  pair  should  be  made  up  of  a  certain 
red  to  be  designated  as  R  and  a  second  red  slightly  differ- 
ent from  the  first  and  designated  as  R'.  A  second  pair 
of  colors  should  be  made  up  by  using  R  and  a  quality  of 


204        LABORATORY  EQUIPMENT  FOR 

red  which  differs  from  it  more  than  R'.  This  third  red 
will  be  designated  as  R".  In  this  way  a  series  of  reds 
can  be  made  up,  all  of  them  differing  from  the  original 
red  R  but  in  increasing  degrees.  R  and  R'  should  now 
be  shown  to  the  reactor  with  R  sometimes  on  the  right- 
hand  side  and  sometimes  on  the  left,  and  he  should  be  re- 
quired to  react  in  every  case  with  the  hand  corresponding 
to  R.  It  will  be  found  that  the  time  required  for  discrimi- 
nation decreases  as  the  difference  between  the  two  qualities 
increases. 

Various  types  of  associations  between  words  may  be 
measured.  The  time  for  so-called  free  association  is  the 
shortest  of  the  association  times.  If  a  word  is  presented 
and  the  reactor  is  required  to  associate  some  other  word 
with  it  but  no  restrictions  whatsoever  are  placed  upon  the 
direction  of  this  association,  we  shall  have  such  pairs  as 
chair — desk,  chair — floor,  chair — table.  A  variety  of  re- 
strictions may  be  imposed  upon  the  reactor.  Thus,  he 
may  be  required  to  name  a  second  object  belonging  to  the 
same  class  as  the  first  object  or  he  may  be  required  to  men- 
tion a  part  of  the  object  named.  He  may  be  required  to 
name  the  general  classes  to  which  the  object  belongs. 
These  restrictive  associations  require  much  longer  time 
than  the  free  associations  and  they  vary  a  great  deal  as 
compared  with  each  other. 

The  experiment  of  striking  out  a's  may  be  made  with 
any  page  of  printed  matter  that  is  conveniently  at  hand. 
For  purposes  of  comparison  in  a  series  of  experiments,  it 
is  desirable  that  the  distance  over  which  the  hand  must 
travel  in  marking  out  a  given  number  of  a's  shall  be  uni- 
form. For  this  reason  it  is  better  to  prepare  tables  which 
are  composed  of  letters  of  the  alphabet  irregularly  arranged 
and  containing  a  standard  number  of  each  one  of  the  letters. 

A  convenient  method  of  preparing  such  tables  was  sug- 


PSYCHOLOGICAL  EXPERIMENTS        205 

gested  by  Dr.  Whipple.  Let  100  printer's  types  of  each 
of  the  letters  to  be  used  be  "pied"  and  then  set  up  as  a 
regular  press  form.  The  form  may  need  a  little  editing 
to  prevent  letters  from  being  repeated  in  close  proximity 
to  each  other,  but  in  general  the  chance  order  of  the  letters 
can  be  accepted  without  further  change. 


EXERCISE  XVII 


A  AND  B — APPARATUS,  PROCEDURE,  AND  RESULTS 


For  the  measurements  of  the  duration  of  writing  ac- 
tivities the  apparatus  and  method  described  on  pages  176- 
180  are  to  be  used.  A  very  simple  form  of  this  apparatus 
can  be  set  up  by  merely  writing  over  a  moving  strip  of 
paper  through  a  sheet  of  carbon  paper.  The  moving  paper 


SIGMAS 
70  — 
60- 
5O  — 
40  — 
30  — 
20  — 
10  — 


I          I 
7         8 

Fio.  109 


I        I        I       I 
12       13       »4       15 


which  receives  the  record  can  be  drawn  along  as  suggested 
on  page  175  by  a  kymograph,  its  rate  being  recorded  by  a 
time  marker.  Figures  109  and  110  show  fluctuations  in 
the  rates  of  movement  during  the  writing  of  different  parts 
of  the  letters  a  and  &.* 

A  recorder  which  will  very  conveniently  show  the  move- 

*  These  two  figures  have  been  supplied  by  Mr.  F.  N.  Freeman  from  a  general 
study  in  which  he  is  engaged.  The  letters  a  and  b  in  the  figures  are  marked  off 
in  sections  which  correspond  to  distances  of  1  mm.  in  the  original  written  letter. 

206 


PSYCHOLOGICAL  EXPERIMENTS        207 


ments  of  different  parts  of  the  hand  during  writing  is  rep- 
resented in  Fig.  111.  It  consists  of  a  spring  A  which  fits 
closely  on  the  hand  and  carries  the  rod  BB.  This  rod 
runs  forward  far  enough  so  that  the  distance  of  its  end 
from  the  wrist  and  elbow  is  the  same  as  the  distance  from 
the  wrist  and  elbow  to  the  pen  held  between  the  thumb 
and  fingers.  This  equality  in  length  insures  a  record  of 
the  hand  and  arm  movement  which  is  on  the  same  scale  as 
the  writing  done  by  the  pen,  and  thus  comparison  is  made 


SIGMAS 


150- 
WO- 
130- 
120- 
110- 
100- 
90- 
80- 
70- 
60- 
50- 
40- 
30- 
20- 
10- 


12345678910 


12    13    14   15    16    17 
FlG.  110 


21    22  23  24  25  26 


direct  and  easy.  At  the  end  of  the  rod  B  is  placed  a  metal 
or  glass  tube  C,  and  through  this  falls  a  tracing  point  DD 
of  the  same  form  as  that  which  has  been  described  under 
Exercise  XIII,  page  170.  The  record  is  made  by  allowing 
the  reactor  to  write  naturally  on  the  paper  with  the  pen 
held  between  the  thumb  and  fingers;  the  tracer  in  the 
meantime  making  a  record  of  all  of  the  movements  which 
the  hand  makes  during  the  writing.  The  written  letters 
are  the  records  of  the  finger  movements  plus  all  of  the  hand 


208        LABORATORY  EQUIPMENT  FOR 

and  arm  movements,  except  such  hand  and  arm  movements 
as  are  made  during  the  intervals  between  the  words,  when, 
of  course,  the  writing  pen  is  raised  from  the  paper.  The 
tracer  is  carried  on  the  paper  by  its  own  weight  and  re- 
cords all  that  the  hand  and  arm  do,  but  gives  nothing  of 
the  pure  finger  movement.  By  a  comparison  of  the 
written  letters  with  the  tracer  record  it  is  easily  possible  to 
determine  what  part  of  the  whole  work  is  done  by  the  hand 
and  arm  and  what  is  done  by  the  fingers.  Two  records 
of  writing  with  their  corresponding  tracer  records  are 

shown  in  Figs.  112 
and  113. 

In  order  to  se- 
cure the  moving 
point  which  is  re- 
quired in  the  third 
part  of  the  experi- 
ment, the  follow- 
ing combination  of 
apparatus  already 
described  may  be 
arranged.  A  belt  of 
paper  is  carried  be- 
tween two  kymograph  drums.  On  this  belt  of  paper  a 
line  is  drawn  obliquely  across  the  paper.  The  belt  is  set 
in  rotation  by  means  of  the  drum,  and  the  reactor  is  allowed 
to  look  at  it  through  a  narrow  slit  in  a  large  shield,  the  slit 
extending  in  a  direction  perpendicular  to  the  direction  of 
movement  in  the  paper.  The  whole  is  represented  in  Fig. 
114,  where  A  B  is  the  belt  and  S  the  shield.  The  shield  is 
intended  to  be  large  enough  so  that  the  observer  sees 
nothing  of  the  belt  beyond  it.  The  shield  thus  prevents 
the  reactor  from  seeing  the  line  on  the  rotating  belt,  but 
gives  him  the  opportunity  of  seeing  the  single  part  of  the 


Fio.  Ill 


PSYCHOLOGICAL  EXPERIMENTS        209 

line  which  lies  directly  under  the  opening  in  the  shield.  As 
the  belt  moves  forward,  the  part  of  the  line  which  the  re- 
actor can  thus  see  will  gradually  move  upward  or  down  ward 

Vutf/V?/   //.B4- 

\J£A  \A!A/  ^--''  ^.« 


i    i 

10  n 


to 


FIG.  112 

along  the  line  of  the  opening  in  the  shield.  If  the  oblique 
line  drawn  across  the  belt  is  a  regular  line,  and  the  drum 
moves  at  a  uniform  rate,  the  point  seen  by  the  reactor  will 
travel  up  and  down  the  slit  at  a  uniform  rate  in  a  given  di- 
rection. Irregularities  in  the  line  will  result  in  irregular 
movements  of  the  points  seen  through  the  slit.  If,  therefore, 


FIG.  113 


it  is  desired  that  the  reactor  strike  at  a  point  which  is  mov- 
ing uniformly,  a  single  line  is  drawn  across  the  moving  belt. 
If  it  is  desired  that  a  certain  change  in  the  rate  of  move- 


210        LABORATORY  EQUIPMENT  FOR 

ment  of  the  point  shall  be  introduced,  irregularities  of  the 
type  indicated  in  Fig.  115  may  be  drawn  in  the  long  line  on 
the  belt  of  paper.  In  order  that  the  effort  to  react  may  be 


FIG.  114 


properly  timed  with  reference  to  the  irregularities  in  the 
line,  a  sounder  may  be  set  up  and  the  signal  to  react  may 
be  given  by  the  experimenter  by  means  of  this  sounder. 

The  movement  of  the  hand  in  aiming  to  strike  this  mov- 
ing point  can  be  studied  in  several  ways.     First,  the  shield 


Fio.  115 


which  covers  the  traveling  line  may  be  made  of  paper  and 
a  carbon  sheet  may  be  placed  under  it.  The  hand  may 
move  across  the  sheet  of  paper,  tracing  a  pencil  line  from 
the  point  of  starting  until  it  reaches  the  point  seen  through 
the  slit.  All  irregularities  in  the  movement  will  thus  be 


Fio.  116 


recorded  on  the  same  paper  as  the  line  which  supplied 
the  point.  Such  a  record  is  shown  in  Fig.  116  in  the  line 
abcdE.  The  reactor  in  this  case  was  directed  to  move  his 


PSYCHOLOGICAL  EXPERIMENTS        211 

pencil  from  the  position  a  where  it  was  held  just  at  the 
bottom  of  the  slit  until  he  could  strike  the  point  traveling 
downward.  It  will  be  noticed  that  he  moves  rapidly  up- 
ward at  first,  then  pauses  and  finally  makes  his  last  move- 
ment with  increasing  rapidity  to  the  end. 

Second,  a  string  may  be  connected  with  the  hand  in  such 
a  way  that  all  forward  movements  of  the  hand  shall  draw 
out  the  string  and  indirectly  make  a  record.  This  method 
does  not  permit  movements  in  different  planes  to  be  re- 
corded without  complicating  the  apparatus  indefinitely. 
Movement  in  one  plane  can,  however,  be  conveniently 
recorded  by  such  a  string.  The  string  should  be  wound 
around  a  cylinder.  This  cylinder  is  supplied  with  an  inner 
coil  spring  which  keeps  the  string  wound  up  under  small 
tension.  It  is  also  fitted  into  a  system  of  cogs  so  that  any 
turning  of  the  cylinder  as  a  result  of  pulling  the  string 
results  in  the  movement  of  a  system  of  wheels  and  ulti- 
mately of  a  pointer.  This  pointer  may  be  allowed  to 
trace  upon  a  smoked  paper,  thus  giving  a  record  of  the 
amount  of  the  hand  movement.  Since  such  an  arrange- 
ment as  this  records  the  hand  movement  only  in  one 
direction,  the  conditions  of  the  experiment  should  be  so 
arranged  that  the  reactor  will  move  his  hand  chiefly  in 
one  plane.  One  of  the  best  directions  in  which  to  allow 
the  string  to  unwind  is  downward  from  directly  above 
the  slot  in  which  the  moving  point  appears. 

C — SUPPLEMENTARY   EXPERIMENTS 

A  device  similar  to  that  described  above  for  recording 
the  movement  of  the  hand  may  be  attached  to  any  part 
of  the  arm  during  writing,  in  order  to  record  the  behavior 
of  this  part  of  the  arm  while  the  fingers  are  forming  the 
letters. 


LM2        PSYCHOLOGICAL  EXPERIMENTS 

A  method  which  has  been  employed  for  the  determina- 
tion of  the  pressure  of  the  different  fingers  during  writing 
consists  in  mounting  on  the  pen  a  number  of  small  tam- 
bours. One  is  placed  under  the  thumb,  one  under  the 
first  finger,  and  one  under  the  middle  finger.  From  these 
various  tambours  connections  are  made  with  recording 
tambours  and  a  triple  record  is  taken  on  a  smoked  surface 
showing  the  various  changes  in  the  pressure  of  each  of 
the  fingers  against  the  writing  pen. 

The  pressure  exerted  by  a  person  writing  on  a  sheet 
of  paper  can  be  readily  measured  by  means  of  the  appa- 
ratus described  on  pages  179-180. 


EXERCISE  XVIII 

No  special  apparatus  is  required  for  Exercise  XVIII. 
It  is  desirable  that  the  figures  to  be  used  in  this  exercise 
should  have  a  sufficient  degree  of  uniformity  to  make  com- 
parison between  the  different  figures  possible.  To  this  end, 
the  figures  should  all  be  made  up  of  the  same  constituent 


FIQ.  117 

lines,  these  being  combined  in  various  different  arrange- 
ments but  having  the  same  absolute  dimensions  and  posi- 
tions in  space. 

A  series  of  tests  of  this  type  is  fully  reported  and  dis- 
cussed in  the  Yale  Psychological  Studies,  New  Series,  Vol. 
I,  No.  2,  pages  349-369. 


213 


214        LABORATORY  EQUIPMENT  FOR 

C — SUPPLEMENTARY   EXPERIMENTS 

There  are  a  number  of  methods  of  recording  the  rate 
of  vibration  of  sung  or  spoken  tones.  The  most  familiar 
methods  are  those  of  the  phonograph.  In  this  apparatus 
a  voice  vibration  is  delivered  against  the  mica  or  glass 
diaphragm.  The  diaphragm  by  means  of  a  sharp  stylus 
cuts  into  a  wax  cylinder,  recording  the  rate  of  the  vibration 
which  is  imposed  upon  the  diaphragm  by  the  voice.  The 
difficulty  of  reading  such  a  record  as  this  prevents  the  use 
of  the  phonograph  for  ordinary  experiments  in  the  psycho- 
logical laboratory.  The  principle  of  the  phonograph  may, 
however,  by  a  slight  modification  be  employed  for  the  pur- 
pose of  making  records  of  voice  reactions. 

Fig.  117  represents  the  apparatus  employed  by  Dr. 
Cameron  in  recording  the  rate  of  voice  vibrations  and  de- 
scribed by  him  in  the  Yale  Psychological  Studies,  Vol.  1, 
No.  2,  page  230,  as  follows: 

"The  recording  apparatus  used  in  the  present  investigation  con- 
sisted of  a  round  rubber  telephone  receiver,  a  vertical  cross  section  of 
which  is  represented  in  Fig.  117.  The  box  (B)  is  provided  with  a 
cover  (C)  of  the  same  material  which  may  be  screwed  tightly  to 
the  face  of  the  box.  Between  the  from  edge  of  the  box  and  the 
cover  is  a  diaphragm  (D)  of  thin  mica,  which  is  held  firmly  in  posi- 
tion by  the  cover,  when  screwed  down.  The  diaphragm  is  5 . 3  cm. 
in  diameter.  Glass  diaphragms  have  also  been  used,  but  with 
less  satisfactory  results. 

"The  cylindrical  chamber  (F)  communicates  directly  with  the  air 
chamber  back  of  the  diaphragm.  An  aluminum  mouthpiece  (P) 
is  attached  to  the  outer  edge  of  (F)  by  a  small  piece  of  rubber  tubing. 
In  the  latter  experiments  a  long  flexible  tube  was  substituted  for  this 
form  of  connection  between  (F)  and  the  mouthpiece  (P) .  A  small  hole 
(R),3  mm.  in  diameter,  is  bored  in  the  mouthpiece  to  allow  the  escape 
of  the  air  forced  into  the  chamber  at  the  moment  the  tone  is  sung. 

"There  is  screwed  to  the  front  of  the  box  a  piece  of  brass  (H), 
shaped  as  shown  in  the  figure,  and  used  for  the  purpose  of  holding 
the  adjustable  screws  M  and  N. 


PSYCHOLOGICAL  EXPERIMENTS        215 

"  M  and  N  are  held  securely  in  position  by  the  set  screws,  V  and 
W.  M  and  N  are  fitted  with  jewel  bearings  in  which  play  the  taper- 
ing ends  of  the  steel  axle  A. 

"To  the  axle  is  attached  the  aluminum  right-angle  piece  KL. 
K  carries  a  straw  (S)  to  the  end  of  which  is  fastened  the  recording 
point  X.  This  point  is  made  of  hammered  brass,  carefully  cut  to  a 
point  and  polished.  Such  a  point  is  fine  enough  to  make  a  sharply 
defined  line  on  smoked  paper,  and  the  lampblack  does  not  adhere 
to  it. 

"The  other  arm  L  is  attached  by  a  joint  to  a  smaller  link  (O)  of 
aluminum,  which  passes  through  an  opening  in  the  middle  of  the 
box  cover  and  is  fastened  to  the  center  of  the  diaphragm  by  a  drop 
of  glue. 

"There  is  thus  provided  a  system  of  continuous  levers  from  the 
outer  surface  of  the  diaphragm  to  the  recording  point,  so  that  move- 
ments of  the  diaphragm  caused  by  the  singing  of  tones  into  the 
mouthpiece  or  by  any  other  means  are  magnified  and  may  be  re- 
corded on  a  belt  of  smoked  paper.  Since  it  is  desirable  to  obtain 
very  long  series  of  records,  a  long  belt  of  smoked  paper  is  used.  The 
belt  passes  between  two  drums  placed  fifteen  feet  apart.  It  is  smoked 
at  one  of  the  drums  and  after  the  record  is  made  is  shellaced  from 
behind." 

Such  a  record  is  reliable  for  determinations  of  pitch. 
It  is  not  useful  in  determining  the  form  of  sound  vibrations. 

A  target  can  be  very  easily  made  of  a  drawing-board 
over  which  has  been  pasted  a  sheet  of  paper  with  concentric 
circles.  A  dart  may  be  made  up  of  a  wooden  shaft  in  the 
end  of  which  has  been  inserted  a  sharp  needle.  The  dart 
should  be  supplied  with  guides  at  the  end  opposite  that 
carrying  the  needle.  These  can  be  made  by  cutting  slots 
in  the  wooden  shaft  and  inserting  cardboard  strips.  The 
record  may  be  taken  by  counting  the  score  as  in  ordinary 
target  practice.  It  is  desirable  also  to  record  not  only 
the  distance  from  the  center  but  also  the  quadrant  in  which 
the  dart  strikes  the  paper. 

The  experiment  which  requires  a  stylus  from  which 
the  reactor  shall  receive  no  sensation  of  pressure  during 


216        PSYCHOLOGICAL  EXPERIMENTS 

writing  may  be  carried  on  by  means  of  the  following  de- 
vice. A  pencil  or  small  wooden  rod  the  size  of  a  pencil, 
is  supplied  at  the  end  with  a  tube  either  of  metal  or  glass, 
and  through  this  tube  is  allowed  to  pass  a  writing  stylus 
of  the  form  described  in  Exercise  XIII.  The  reactor  will 
receive  no  pressure  sensations  from  this  pen,  as  the  writing 
stylus  is  free  to  move  upward  and  downward  in  the  tube. 
The  downward  movement  of  the  wooden  rod  will  simply 
result  in  the  sliding  of  the  tube  down  the  writing  stylus. 
Experiments  tried  with  such  a  stylus  by  a  reactor  who 
tries  to  write  with  his  eyes  closed  indicate  very  clearly  the 
results  of  withdrawing  both  visual  and  tactual  sensations 
in  writing  activities  and  in  the  activities  of  drawing. 


EXERCISE  XIX 

V 
A — APPARATUS   AND   PROCEDURE 

The  apparatus  necessary  for  the  first  part  of  this  experi- 
ment has  been  fully  described  in  connection  with  Exercise 
XIV  (see  page  175). 

The  second  experiment  requires  no  equipment  other 
than  a  mirror  and  some  patterns.  It  should  be  noted,  per- 
haps, that  simple  geometrical  patterns  such  as  stars  and 
rhomboids  are  better  for  the  purposes  of  this  exercise  than 
more  complex  forms. 

A  convenient  method  of  preparing  cards  for  the  third 
part  of  this  exercise  is  to  secure  plain  cards  and  mark 
them  with  numerals,  or  paste  on  them  kindergarten  pict- 
ures or  small  pieces  of  colored  paper  which  will  be  suffi- 
cient to  distinguish  them. 

B — RESULTS 

The  following  table  shows  the  changes  in  the  length  of 
contacts  and  intervals  between  contacts  during  practice 
with  the  unnatural  or  reverse  order  of  finger  movements. 
The  first  horizontal  column  shows  the  rate  before  practice. 
The  second  horizontal  column  shows  the  averages  of  ten 
cases  after  200  trials.  The  third  shows  the  average  of  ten 
cases  after  400  trials,  and  the  last  shows  the  average  of 
ten  cases  after  600  trials. 

217 


218         LABORATORY  EQUIPMENT  FOR 


At  first  .  .  . 
After  200. 
After  400  . 
After  600. 

Finger 
Index 

PMM 

after 

Finger 

(Middle) 

Pause 
after 
II 

AVK- 

M.V. 

2.1 
3.1 
3.4 

2.8 

Avg. 

M.V. 

Avg. 

M.V. 

Avg. 

M.V. 

93 
90 
87 
91 

127 
100 

92 

99 

7.7 
8.6 
8.3 
8.1 

89 
92 

84 
87 

2.4 
2.7 
1.6 
1.9 

102 
95 
90 
91 

5.7 
5.2 
5.5 
6.1 

At  first  

Figpr 

Pause 

•ST 

Fifr 

Avg. 

M.V. 

Avg. 

M.V. 

Avg. 

M.V. 

124 

111 

114 
109 

7.1 

7.7 
6.4 
5.1 

72 
71 
64 
60 

3.1 

2.7 
2.2 
3.0 

101 

97 
96 
93 

4.4 
4.7 
3.5 
3.1 

After  200.  . 

After  400 

After  600.. 

The  following  table  shows  improvement  both  in  time 
and  accuracy  in  following  in  five  successive  trials  the  same 
four-line  pattern  when  the  pattern  was  seen  in  a  mirror. 


Corrective    Movements 

Line 

1234 

Trial 

Time  in 
seconds 

Totals 

1 

97 

4 

7 

3 

4 

18 

2 

46 

6 

2 

5 

1 

14 

3 

31 

3 

3 

2 

3 

11 

4 

20 

0 

4 

1 

3 

8 

5 

22 

1 

2 

1 

1 

5 

The  following  table  shows  the  time  for  10  successive 
distributions  of  eighty  cards  which  were  marked  with  the 
numerals  from  1  to  8.  The  spatial  order  of  these  cards 
in  the  first  series  of  distributions  was:  5-3-6-1-8-4-7-2. 


Distribution 1      2      3      4      5      6      7      8      9     10 

Time  in  seconds..   .  .84  71  67  54  50  52  57  60  51  57 


PSYCHOLOGICAL  EXPERIMENTS        219 

When  the  order  was  changed  to  6-4-3-7-5-2-1-8,  the 
time  of  distribution  for  the  first  trial  was  92  seconds  with 
many  tendencies  to  return  to  the  first  order. 

C — SUPPLEMENTARY   EXPERIMENTS 

Experiments  with  writing  seem  to  show  that  the  time 
of  writing  for  a  given  subject  suffers  little  change  from 
trial  to  trial. 

The  simplest  method  of  studying  the  control  of  the 
winking  reflex  is  to  hold  before  the  eye  a  piece  of  glass 
and  allow  the  experimenter  to  strike  the  glass  directly  in 
front  of  the  eye.  The  degree  of  control  will  be  shown  by 
recording  the  number  of  times  during  which  the  observer 
is  capable  of  resisting  the  reflex  tendency  to  wink  when 
the  glass  is  struck,  the  glass  being  held  in  the  successive 
trials  at  various  distances. 

Methods  of  working  with  the  typewriter  will  suggest 
themselves  to  any  one  who  is  unfamiliar  with  the  manipu- 
lation of  this  machine.  Simple  copying  of  prose  passages 
and  a  measurement  of  the  time  required  for  a  given  number 
of  letters,  together  with  the  errors  in  these  letters,  serve 
very  well  to  indicate  the  progress  of  the  reactor  who  be- 
gins without  previous  training.  The  machine  may  be 
utilized  for  experiments  even  by  experts  if,  instead  of 
using  the  regular  letters  on  the  keyboard,  certain  colors 
or  outline  forms  are  substituted  for  the  familiar  keys. 
Each  reaction  will  in  this  case  be  recorded  as  a  letter,  while 
the  stimulus  received  by  the  reactor  will  not  be  a  letter 
but  the  color  or  outline  figure  with  which  the  key  is  cov- 
ered. 


EXERCISE  XX 

A — APPARATUS  AND   PROCEDURE 

The  apparatus  required  for  recording  taps  has  been  de- 
scribed in  connection  with  Exercise  XIV,  page  175. 

A  metronome  can  be  purchased  at  any  establishment 
which  sells  musical  instruments  or  from  C.  H.  Stocking 
Co. 

B — RESULTS 

Table  I  shows  some  effects  of  distraction.  The  aver- 
ages are  in  sigmas. 


Average   normal 

time  for  tapa 

1 
1 

without  dis- 
traction, meas- 
ured by  taking 

Fast  met- 
ronome 

Slow  met- 
ronome 

Movement 
of  other 
hand 

Reading 

0 

time  of  five 

successive  taps 

Avg.    M.V. 

Avg.   M.V. 

Avg.   M.V. 

Avg.  M.V. 

Avg.    M.V. 

A 

183    6.3 

211    9.3 

218    7.5 

238  11.4 

193    7.7 

B 

197    4.4 

209    8.3 

207  13.2 

254  10.1 

215    6.5 

The  following  results  show  the  effects  of  fatigue.  The 
first  five  taps  in  every  50  were  counted  and  the  total  time 
was  found  as  follows: 

910  sigmas,  920,  940,  900,  900,  880,  740,  970,  1,000,  1,240,   1,050, 
1,070,  1,080,  1,080,  1,300,  1,100,  1,095. 


C — SUPPLEMENTARY   EXPERIMENTS 

Apparatus  and   methods  for  the  first  supplementary 

experiment  are  described,  and  reference  to  a  complete  ex- 

220 


PSYCHOLOGICAL  EXPERIMENTS        221 

periment  of  this  type  is  given  under  Exercise  XVIII  (see 
pages  214  and  215). 

The  apparatus  necessary  for  the  exercise  on  muscular 
fatigue  consists  of  a  dynamometer  such  as  already  described 
under  Exercise  XIII.  Such  a  dynamometer  may  be  used 
continuously  for  a  longer  period  of  time,  and  a  record 
taken  of  the  amount  of  work  done  by  the  reactor.  If 
the  work  is  continued  until  the  reactor  is  no  longer  able 
to  move  the  dynamometer,  the  records  will  show  the  total 
amount  of  work  necessary  to  produce  complete  fatigue.  If 


Fia.  118 
From  the  catalogue  of  C.  H.  Stoelting  Co.,  Chicago 

the  work  is  not  continued  for  a  sufficient  period  of  time 
to  produce  complete  fatigue,  the  falling  off  in  the  records 
of  the  movements  will  show  the  increasing  tendency 
towards  fatigue.  The  disadvantages  of  using  a  dyna- 
mometer for  such  experiments  is  that  it  is  extremely  diffi- 
cult to  secure  a  record  of  the  total  amount  of  work  done. 
Other  forms  of  instruments  have  accordingly  been  devised 
for  recording  and  automatically  measuring  the  amount  of 
work  a  reactor  can  do.  Mosso's  Ergograph,  which  is  one 
of  the  best  known  instruments,  is  represented  in  Fig.  118. 


222        LABORATORY  EQUIPMENT  FOR 

This  consists  of  a  sliding  bar  connected  with  a  weight  at  one 
end  and  a  finger  holder  at  the  other  end.  The  sliding  bar 
is  attached  to  a  pointer  which  can  trace  upon  a  kymo- 
graph surface.  The  experiment  consists  in  allowing  the 
reactor  to  move  his  finger  so  as  to  lift  the  weight  as  long 
as  it  is  possible  for  him  to  make  any  movement  against 
the  weight.  The  pointer  records  the  form  and  extent  of 
this  movement  upon  the  drum.  An  addition  for  the  pur- 
pose of  measuring  the  amount  of  movement  can  be  made 
in  the  form  of  an  automatic  tape  take-up  which  will  draw 

up  a  tape  each  time 
the  weight  is  lifted. 
During  the  test  the 
hand  and  arm  of  the 
reactor  are  held  rigidly 
in  position,  so  as  to 
eliminate  as  far  as  pos- 
sible the  movements 
of  all  muscles  except 
those  which  are  being 
tested.  The  objection 
to  such  a  weight  ergo- 
graph  is  that  at  the 
end  of  a  given  experi- 
ment the  finger  can  undoubtedly  do  some  work,  even 
though  it  can  not  do  what  it  is  required  to  do  when 
the  demand  is  made  that  it  lift  the  large  weight  which  is 
connected  with  the  apparatus.  The  finger  is  in  a  con- 
dition in  which  it  seems  to  be  unable  to  do  further  work, 
not  because  it  is  completely  exhausted  but  because  it  is 
too  exhausted  to  do  the  large  amount  of  work  demanded. 
The  remedy  for  this  defect  of  the  weight  ergograph  is  to 
be  found  in  substituting  for  the  weight  a  spring.  If  now 
the  reactor  is  allowed  to  pull  against  the  spring  instead  of 


•I 


Fio.  119 


From  the  catalogue  of  C.  H.  Stocking  Co., 
Chicago 


PSYCHOLOGICAL  EXPERIMENTS        223 

against  a  fixed  weight,  his  early  movements  will  indicate 
the  absence  of  fatigue  in  the  length  of  the  movement. 
Later,  the  movements  will  grow  smaller  and  smaller,  and 
the  amount  of  work  demanded  for  each  one  of  these  small 
movements  will,  because  the  reactor  is  working  against  a 
spring,  be  reduced  in  quantity.  The  rate  at  which  the 
reactor  makes  the  movements  should  in  all  cases  be  a  uni- 
form rate  determined  by  a  metronome  which  gives  the 
signals  for  reaction. 

A  simple  ergograph  supplied  with  the  Harvard  physio- 
logical apparatus  and  shown  in  Fig.  119  can  be  used  in 
securing  fatigue  records  from  the  index  finger. 

More  elaborate  forms  of  ergographs  have  been  devised. 
These  elaborate  forms  are  designed  to  secure  greater  isola- 
tion of  the  muscles  exercised.  It  is  possible  in  most  of 
the  simple  ergographs  for  the  finger  which  is  called  upon 
to  do  the  work  to  receive  much  assistance  from  the  other 
parts  of  the  hand  and  arm  which  it  is  not  intended  to 
test.  An  elaborate  device  is  described  by  Professor 
Bergstrome  in  the  American  Journal  of  Psychology,  Vol. 
XIV,  1903,  pp.  510-540. 


EXERCISE  XXI 

A — APPARATUS  AND   PROCEDURE 

The  best  method  of  making  up  series  of  nonsense  syl- 
lables consists  in  preparing  a  large  number  of  such  syllables 
on  separate  slips  of  paper.  These  syllables  should  be 
made  up  as  follows:  Start  with  the  first  consonant  in 
the  alphabet  and  the  first  vowel.  Set  down  as  the  third 
letter  of  the  syllable  each  of  the  succeeding  consonants  of 
the  alphabet.  Thus,  we  have  bac,  bad,  baf,  bag,  etc.  A 
second  series  should  be  prepared  beginning  with  the 
second  consonant  of  the  alphabet  as  the  first  letter  of  the 
syllable.  Add  the  first  vowel,  and  in  succession  each  of 
the  remaining  consonants  of  the  alphabet.  Thus  we 
should  have  cab,  cad,  caf,  cag,  etc.  Another  series  of 
variations  can  be  produced  by  changing  the  vowel.  Thus, 
the  first  combinations  in  the  series  would  be  bee,  bic,  boc, 
buc.  In  like  fashion  we  should  proceed  with  ceb,  cib,  cob, 
cub.  After  this  series  has  been  prepared,  such  combina- 
tions as  "bad"  and  "bag"  should  be  thrown  out  because 
they  represent  words.  Such  combinations  as  "caf" 
should  also  be  stricken  out  because  they  resemble  too 
closely  common  words  of  the  language.  After  a  series 
of  combinations  has  been  prepared  by  selecting  non-sig- 
nificant forms,  the  whole  collection  should  be  placed  in  a 
box  and  thoroughly  mixed.  Any  desired  number  may  now 
be  drawn  from  this  thoroughly  mixed  collection  and  the 
character  of  the  material  will  be  sufficiently  uniform  for 
experimental  purposes.  The  following  list  presents  a  few 
such  syllables  which  may  be  used  in  some  of  the  simpler 

224 


PSYCHOLOGICAL  EXPERIMENTS        225 

exercises  without  the  more  elaborate  preparation  described 
above: 

Dap,  Vac,  Jaf,  Lar,  Bex,  Bup,  Nat,  Hif,  Lis,  Mor,  Cul, 
Zuc,  Jut,  Puj,  Riv,  Sal,  Mik,  Tex,  Pij,  Hoj,  Dae,  Cib,  Rev, 
Bir,  Huv,  Vog,  Gir,  Jal,  Kod,  Dak,  Pon,  Sab,  Def,  Dor, 
Miv,  Mel,  Jub,  Lig,  Biz,  Gar,  Cem,  Vub,  Har,  Dik,  Rej, 
Ber,  Lun,  Hak,  Jec,  Fij,  Ked,  Tol,  Soc,  Gee. 

If  experiments  are  to  be  performed  with  these  syllables, 


FIG.  120 
From  the  catalogue  of  Z im merman n,  Leipzig,  Germany 

it  is  desirable  that  they  should  be  quite  legible.  To  this 
end  they  should  be  printed  or  copied  on  a  typewriter  or 
made  up  of  gummed  letters  which  have  been  pasted  on 
cards.  The  cards  may  now  be  read  off  in  series,  each  one 
being  exposed  to  view  by  drawing  off  the  one  above  it  in 
a  pack  held  in  the  hand. 

The  rate  at  which  the  syllables  are  exposed  is  a  matter  of 
some  importance.     A  device  for  securing  greater  uniform- 


226        LABORATORY  EQUIPMENT  FOR 

ity  of  exposure  than  can  be  attained  by  simply  handling 
the  cards,  is  to  paste  the  syllables  on  a  kymograph  and 

allow  them  to  be  seen 
through  an  opening  in  a 
screen  as  the  kymograph 
is  rotated  with  a  slow, 
steady  motion.  This 
method  has  the  disad- 
vantage of  keeping  the 
letters  in  constant  motion 
during  the  whole  period 
of  exposure.  A  second 
device  consists  of  a  drum 
which  is  moved  forward 

From  the  catatogue  of  Zimmermann,  by  means  of  a  Weight  and 

Leipzig,  Germany  ,     , 

a  pendulum  escapement. 

An  electrical  device  for  moving  the  drum  forward  at 
regular  intervals  is  described  by  Professor  Bergstrome  in 
the  American  Journal  of 
Psychology,  1907,  pp.  206- 
238.  A  pendulum,  instead 
of  acting  directly  upon  the 
drum,  acts  by  means  of  an 
electric  circuit  which  it 
makes  with  each  oscillation. 
The  apparatus  may  be  com- 
plicated by  the  addition  of 
a  second  pendulum  so  con- 
nected with  the  first  that  the 
intervals  of  movement  in  the 
drum  shall  be  regulated  dif- 
ferently during  the  exposure 
of  the  syllables  and  during  the  intervals  between  exposures. 

A   very   elaborate   mechanism   has   been   devised    by 


FIG.  122 

From  the  catalogue  of  Zimmermann, 
Leipzig,  Germany 


PSYCHOLOGICAL  EXPERIMENTS        227 

Professor  Wirth,  of  Leipzig.  It  is  shown  in  Figs.  120-121. 
In  Fig.  120  A  the  apparatus  is  cased  in  and  a  single  word 
appears  as  seen  by  the  observer.  In  Fig.  120  B,  the  tape 
with  syllables  and  the  wheel  on  which  this  tape  moves 
is  shown.  In  Fig.  121  the  weights  and  electrically  con- 
trolled escapement  for  the  apparatus  are  shown.  When  a 
current  is  passed  through  the  electromagnets  the  syllables 
move  forward.  The  rate  of  this  movement  is  determined 
by  the  apparatus  which  sends  the  electric  current  into  the 
magnets.  This  controlling  apparatus  is  the  pendulum 
shown  in  Fig.  122.  By  means  of  adjustable  bobs  the  rate 
of  this  pendulum  can  be  varied  within  wide  limits.  By 
means  of  contacts  placed  along  the  scale  shown  at  0, 
C,  C,  0,  in  the  figure  the  current  can  be  sent  as  desired 
to  the  escapement  apparatus. 

B — RESULTS 

Table  showing  individual  differences  and  differences 
in  the  same  individual  under  varying  conditions. 

Readings  required  to  learn  ten  syllables. 


Observers 

Read 
silently 

Read 
aloud 

Hear 
read 

Heard 
and  seen 

A 

15 

8 

18 

17 

B 

6 

5 

5 

5 

C 

6 

7 

6 

8 

D 

11 

10 

14 

9 

Table  showing  readings  on  first  learning  and  after  one 
hour. 


Observer 

Readings 
(silently) 
first  time 

After 
one 
hour 

A 

15 

3 

B 

6 

2 

C 

6 

3 

228        PSYCHOLOGICAL  EXPERIMENTS 

Table  showing  difficulty  of  learning  series  of  different 
lengths,  all  read  silently. 


Observer 

No.  of  syllables 

10 

15 

25 

A 

15 

27 

not  lc>:iniod  at 

50 

B 

6 

12 

48 

C — SUPPLEMENTARY   EXPERIMENTS 

The  monochord  required  for  memory  of  tones  is  de- 
scribed on  page  111. 

For  the  other  supplementary  experiments,  no  special 
apparatus  is  required. 


EXERCISE  XXII 

A — APPARATUS   AND   PROCEDURE 

Equivocal  figures  such  as  are  required  for  the  first  part 
of  the  exercise  are  shown  in  Fig.  123,  A  and  B.  The 
record  of  the  rate  of  fluctuation  in  these  figures  can  be 
taken  by  means  of  a  key  such  as  that  described  on  page 
175  and  an  electric  marker  such  as  that  described  on 
page  155.  The  observer  is  required  to  press  down  upon 


FIG.  123a 

the  key  when  the  figure  appears  in  its  first  position  and  to 
lift  the  finger  when  the  figure  reverses.  In  some  cases  it 
may  be  necessary  to  record  more  than  two  types  of  experi- 
ence. In  this  case  either  two  markers  and  two  keys  can 
be  employed,  or  a  code  of  signals  can  be  worked  out  to  be 
operated  by  the  single  key  and  marker. 

229 


230        PSYCHOLOGICAL  EXPERIMENTS 

For  the  experiments  on  retinal  rivalry  a  lens  stereoscope 
can  be  used.  (See  pages  93  and  94.) 

A  Masson  disk  is  represented  in  Fig.  124.  It  consists 
of  a  white  disk  marked  at  intervals  with  black  lines  which 


Flo.  1236 

have  all  the  same  absolute  width.  The  relative  width  of 
the  successive  lines  as  compared  with  the  white  area  which 
is  mixed  with  the  black  when  the  disk  is  rotated,  grows 
constantly  less  from  the  center  outward.  The  result  is 
that  the  gray  rings  which  appear  when  the  disk  is  rotated, 


Fio.  124 


grow  lighter  and  lighter  from  center  to  circumference  of  the 
disk.  One  ring  will  be  found  that  is  only  intermittently 
visible.  This  is  the  ring  for  which  a  record  should  be 
taken. 


EXERCISE  XXIII 

A — APPARATUS   AND   PROCEDURE 

The  apparatus  necessary  for  this  exercise  can  be  de- 
scribed best  by  exhibiting  at  the  outset  a  complete  form  of 
the  complication  pendulum.  Substitute  devices  of  a  sim- 
pler character  can  be  made  on  the  same  general  principle. 
Fig.  125  shows  the  complex  form  of  complication  pendu- 
lum described  by  Wundt.  It  consists  in  a  pendulum 
PL  the  upper  end  of  which  is  coupled  by  means  of  a  cog- 
wheel with  the  pointer  Z.  Whenever  the  pendulum  os- 
cillates, the  pointer  Z  moves  in  front  of  a  scale  S.  When 
the  pendulum  is  in  use,  all  of  the  mechanism  behind  the 
dial  is  hidden  so  that  the  observer  can  see  nothing  but 
the  scale  arid  pointer  Z  as  it  moves  backward  and  forward 
across  the  scale.  By  means  of  an  adjustable  connection, 
a  bell  can  be  sounded  or  an  electric  circuit  closed  when 
the  pointer  is  at  any  desired  point  on  the  scale.  The  ex- 
periment consists  in  setting  the  bell  so  that  it  sounds  when 
the  lever  is  at  a  given  point  on  the  dial,  and  requiring  the 
observer  to  determine  the  position  of  the  pointer  on  the 
scale  at  the  instant  when  the  bell  sounds.  The  rate  of 
the  pointer's  movement  can  be  modified  by  shortening 
or  lengthening  the  pendulum  P. 

Simpler  forms  of  apparatus  can  be  devised.  For  ex- 
ample, an  ordinary  metronome  can  be  employed,  the 
pointer  passing  behind  an  opening  in  a  shield,  the  opening 
having  graduations  so  that  the  position  of  the  pointer 
behind  the  shield  can  be  easily  read.  The  sounder,  which 
is  always  a  part  of  the  metronome,  can  be  related  to  differ- 

231 


Fio.  125 

From  Wundt's  "  Grundziige  der  physiologischen  Psychologie 
5th  Ed.,  Vol.  Ill,  p.  82 
232 


Fio.  126 


PSYCHOLOGICAL  EXPERIMENTS        233 

ent  points  on  the  scale  by  tipping  the  metronome  into 
various  positions  so  as  to  give  the  sound  at  various  parts 

of  the  scale.  The  experi- 
ment consists  in  requiring 
the  observer  to  determine, 
as  before,  at  what  point  on 
the  scale  the  sound  is  pro- 
duced. 

A  complication  instru- 
ment designed  by  Prof.  A. 
H.  Pierce  and  described  by 
him  as  follows,  serves  the 
purposes  of  this  experiment 
very  well:  "In  Fig.  126 
AAAA  are  card-holders  at 
the  ends  of  rigid  arms,  90° 

apart,  attached  to  the  main  axis  of  rotation.  BBBB  are 
light  steel  rods,  tipped  with  platinum  wire,  attached  to  a 
collar  which  rotates  on  the  main  axis  behind  the  card-car- 
rying arms,  and  which  can  be  set  at  any  point  by  a  screw. 
The  platinum  tips  pass 
through  a  meniscus  of  mer- 
cury, the  latter  being  con- 
tained in  a  well  in  the  wooden 
block  C.  Thus  a  sounder,  or 
telephone,  is  electrically  actu- 
ated. In  practice,  the  B's 
are  somewhere  behind  the 
;l's.  The  cards  to  be  placed 
in  the  holders  are  graduated 
as  desired." 

"Fig.  127  shows  the  front 

screen  in  place.     This  is  all  that  is  seen  by  the  observer. 
A  vertical  thread  is  placed    in  the  window  at  the  exact 


FIG.  127 


234         LABORATORY  EQUIPMENT  FOR 

point  where  the  sound  comes.  The  subject  notes  the 
mark  on  the  card  which  seems  to  be  immediately  behind 
this  thread  at  the  instant  of  hearing  the  sound.  The 
actual  objective  simultaneity  is  determined  empirically." 
Certain  simple  forms  of  exposure  apparatus  are  de- 
scribed on  page  197.  These  can  be  converted  into  de- 
vices which  first  expose  and  then  cover  up  what  they  have 
exposed,  by  placing  the  figures  or  light  so  that  they  will 
be  uncovered,  not  at  the  end  of  the  movement,  but  in  the 


Fio.  128 

middle  of  the  movement.  Other  forms  which  may  be 
mentioned  consist  of  long  pendulums  which  carry  screens 
with  openings  of  any  desired  length.  Such  pendulum 
tachistoscopes  are  open  to  the  objection  that  they  distract 
the  observer  by  their  movement.  A  form  of  tachistoscope 
which  is  free  from  the  objection  of  a  moving  surface  has 
been  described  by  Professor  Dodge.  It  consists  in  a  box 
represented  in  Fig.  128.  This  box  has  two  openings  at 
Wl  and  W2  through  which  light  from  a  convenient  source 


PSYCHOLOGICAL  EXPERIMENTS        235 

may  be  allowed  to  pass.  The  light  from  W2  strikes  a 
mirror  M2  and  is  reflected  to  a  surface  O2,  which  is  one 
field  upon  which  letters  or  numbers  or  other  desired  ob- 
jects may  be  exposed.  The  light  from  O2  passes  along 
the  line  02F  to  the  opening  in  front  of  which  the  observer's 
eye  has  been  placed.  In  the  course  of  the  line  FO2  is 
placed  a  piece  of  dark  glass  TS.  This  dark  glass  is  not 
as  transparent  as  ordinary  glass  and  reduces  somewhat 
the  light  from  O2.  Nevertheless,  it  is  sufficiently  trans- 
parent to  give  an  adequate  light  from  the  field  O2  and  its 
chief  purpose  is  served,  not  in  connection  with  the  light 
that  comes  through  the  opening  W2,  but  in  connection 
with  the  light  which  comes  through  the  opening  W1.  If 
now  the  light  is  allowed  to  enter  the  box  through  the  open- 
ing W1  rather  than  through  the  opening  W2,  it  will  be  re- 
flected from  the  mirror  Ml  to  the  field  O1,  and  from  O1 
the  light  passes  to  the  dark  glass  TS.  From  the  surface 
of  the  dark  glass,  the  light  is  reflected  into  the  eye  of  the 
observer.  A  certain  amount  of  light  also  passes  through 
this  dark  glass  to  the  back  surface  from  which  it  is  in  turn 
reflected  into  the  eye  of  the  observer,  but  it  loses  so  much 
intensity  in  its  double  passage  through  the  dark  glass 
that  the  image  from  the  back  surface  is  practically  lost  and 
does  not  attract  the  attention  of  the  observer.  The  field  O1 
is  by  this  means  directly  superimposed  upon  the  field  O2. 
By  an  adjustment  of  the  openings  W1  and  W2  the  inten- 
sity of  the  two  fields  may  be  made  equal  to  each  other. 
A  suitable  device  may  be  provided  for  changing  the  illu- 
mination from  W1  to  W2,  or  in  the  converse  direction. 
For  example,  a  pendulum  may  be  allowed  to  swing  in 
such  a  way  that  an  upper  shield  will  cover  the  opening 
W1  for  a  time,  and  a  lower  shield  which  is  allowed  to  pass 
by  W2  will  allow  the  light  to  enter  through  W2  for  any  de- 
sired length  of  time.  As  the  pendulum  swings  further, 


236         LABORATORY  EQUIPMENT  FOR 

the  lower  shield  may  be  made  to  cover  the  opening  W2\ 
while  the  upper  shield  is  opened  so  as  to  allow  the  light 
to  enter  through  Wl.  While  the  light  is  coming  only 
through  the  opening  Wl,  the  field  O1  will  be  in  clear  view 
and  the  field  O2  will  be  invisible.  As  soon  as  the  entrance 
of  the  light  is  changed  by  the  movement  of  the  pendulum, 
the  fields  are  reversed  and  O2  comes  into  view  to  the  ex- 
clusion of  O1.  The  appearance  of  the  fields  in  this  case 
is  without  visible  movement  at  any  point,  and  the  chief 
objection  to  the  various  forms  of  fall-tachistoscopes  is 
entirely  obviated. 

Experiments  which  require  series  of  sounds  given  with 
regularity  at  short  intervals  can  be  set  up  with  a  metro- 
nome. They  can,  however,  be  properly  carried  out  only 
with  the  aid  of  complex  apparatus.  Fig.  72  (page  145) 
showed  an  attachment  for  the  Ludwig  Kymograph  for 
the  purpose  of  utilizing  that  apparatus  to  make  and 
break  electric  circuits  which  in  turn  operate  sound  ham- 
mers or  spark  devices.  The  wheel  shown  at  the  left  of  the 
figure  is  connected  with  the  shaft  of  the  clock-work.  Con- 
tacts may  be  distributed  along  the  graduated  scale  at 
known  intervals,  and  from  these  contacts  electric  currents 
may  be  carried  at  desired  intervals  to  properly  arranged 
stimulating  devices. 

A  simple  form  of  apparatus  which  serves  many  purposes 
in  giving  successive  stimulations  is  a  heavy  pendulum 
swinging  past  a  long  graduated  scale  such  as  that  shown 
in  Fig.  122  (page  226).  The  scale  should  be  graduated 
into  time  units. 

An  elaborate  apparatus  for  working  with  time  inter- 
vals was  designed  by  Schumann.  This  apparatus  is 
driven  by  means  of  the  Helmholtz  rotation  apparatus  de- 
scribed on  page  146.  It  consists  of  a  graduated  disk 
upon  which  are  fastened  a  number  of  contacts,  one  or 


PSYCHOLOGICAL  EXPERIMENTS        237 

more  of  which  can  be  easily  moved  so  as  to  regulate  in 
the  course  of  the  experiment  the  interval  between  con- 
tacts. A  central  arm  connected  with  the  rotation  appa- 
ratus moves  over  these  contacts  at  a  regular  rate,  and  the 
current  thus  made  and  broken  is  conducted  to  a  sound 
hammer  or  other  suitable  device,  where  it  is  transformed 
into  a  stimulus  for  one  or  the  other  of  the  senses. 

The  apparatus  for  recording  the  efforts  of  the  subject 
to  reproduce  such  a  series  of  stimuli  is  the  same  as  that 
required  for  the  record  in  connection  with  the  equivocal 
figures  in  the  last  exercise.  If  it  is  desired  that  the  repro- 
duction of  the  series  of  stimulations  shall  be  complete,  not 
only  a  key  and  marker  should  be  used,  but  provision  should 
be  made  for  the  reactor  to  hear  a  series  of  sounds  which 
correspond  to  his  own  movements.  This  series  of  sounds 
can  be  secured  by  connecting  a  sound  hammer  with  the 
circuit  between  the  reaction  key  and  the  marker. 

B — RESULTS 

In  general  it  will  be  found  that  the  sound  produced 
in  a  complication  series  is  always  referred  to  a  wrong 
point  in  the  visual  series.  Indeed,  the  experiment  was 
suggested  by  the  fact  that  the  older  astronomical  observa- 
tions in  which  the  observer  was  required  to  compare  a 
visual  and  auditory  series,  always  showed  more  or  less 
error,  so  that  sound  and  light  were  never  reported  in  their 
true  objective  relation.  No  general  statement  can  be  made 
with  regard  to  the  type  of  error  which  will  be  committed 
in  the  experiments,  as  the  direction  and  extent  of  the  error 
depend  very  largely  upon  individual  tendencies. 

The  other  experiments  show  the  increase  in  scope  of 
consciousness  through  grouping  of  experiences,  and  the 
impossibility  of  recognizing  correctly  a  large  series  of 
impressions  either  when  given  simultaneously  or  succes- 


238        PSYCHOLOGICAL  EXPERIMENTS 

sively.  In  broad  general  terms  it  will  be  found  that  the 
range  of  accurate  recognition  is  limited  to  from  six  to 
ten  impressions,  if  these  are  given  in  such  a  way  as  to 
render  rhythmical  grouping  impossible. 

C — SUPPLEMENTARY   EXPERIMENTS 

The  simplest  experiment  in  time  perception  which  can 
be  performed  is  to  give  the  observer  a  succession  of  three 
stimulations,  the  first  two  of  which  shall  be  separated  by 
a  standard  interval,  the  second  and  the  third  by  a  variable 
interval.  If  this  variable  interval  is  successively  increased 
and  decreased,  a  determination  can  be  made  of  the  limits 
of  accurate  recognition  of  intervals.  It  will  also  be  found 
by  a  similar  experiment  that  the  accentuation  of  any  one 
of  the  stimuli  in  the  series  modifies  the  estimation  of  the 
interval  preceding  and  succeeding  the  accentuated  stimulus. 

If  it  is  desired  to  use  a  continuous  sound  it  will  be 
found  possible  to  produce  such  a  sound  by  shunting  an 
electric  tuning-fork  into  a  telephone  circuit.  The  result 
will  not  be  a  musical  tone  in  the  telephone,  but  rather  a 
burr  which  results  from  a  rapid  succession  of  makes  and 
breaks  in  the  electromagnet  in  the  telephone.  It  is  ex- 
tremely difficult  to  control  a  continuous  sound  of  any 
ordinary  type.  The  sound  of  a  tuning-fork  is  not  loud 
enough  to  act  upon  a  telephone  in  a  remote  room  and  be 
transmitted  as  a  musical  note  to  the  telephone  near  the 
observer.  Any  other  form  of  transmission  than  the 
electric  suffers  from  the  impossibility  of  instantly  shunting 
off  the  sound.  There  must  be  some  continuous  medium 
between  the  source  of  the  sound  and  the  observer  in  such 
a  case,  and  this  continuous  medium  almost  invariably 
conducts  enough  of  the  vibration  so  that  the  observer  is 
more  or  less  distracted  before  and  after  the  strong  stimu- 
lus which  is  the  subject  of  the  investigation. 


EXERCISE  XXIV 

A — APPARATUS   AND   PROCEDURE 

The  apparatus  for  this  experiment  can  be  made  very 
simply.  A  strip  of  black  cardboard  may  be  passed 
through  two  openings  lying  in  the  same  horizontal  line  in 
a  white  cardboard.  Instead  of  a  strip  of  black  card- 
board some  flexible  material,  such  as  a  coarse  thread, 
may  very  easily  be  employed;  or  a  narrow,  firmly  woven 
braid  will  serve  the  purpose  very  well.  Extending  ver- 
tically across  the  portion  of  the  black  strip  or  thread 
which  is  visible  to  the  observer,  should  be  the  short 
cross-line  described  in  the  text.  The  observer  can  now, 
by  reaching  behind  the  white  cardboard,  draw  the  black 
strip  with  its  vertical  cross-line  either  to  the  right  or  to 
the  left,  and  in  this  way  adjust  the  cross-line  at  any  de- 
sired distance  from  the  points  where  the  line  is  cut  off  by 
the  cardboard. 

A  second  method  of  setting  up  this  experiment  is  to  use 
the  apparatus  described  under  Exercise  I  for  the  measure- 
ment of  illusions.  A  horizontal  line  is  drawn  on  the  fixed 
card  and  a  short  black  line  is  exposed  from  behind  a  white 
screen,  the  cross-line  and  the  screen  being  attached  to  the 
movable  board  in  the  apparatus.  The  short  cross-line 
is  now  adjusted  to  the  desired  position  along  the  long 
horizontal  line.  The  cross-line  may  be  drawn  on  the 
back  of  a  glass,  in  which  case  there  will  be  no  lines  in  the 
field  of  vision  except  those  which  are  to  be  compared. 

For  the  second  part  of  this  experiment,  the  simplest 
method  consists  in  laying  before  the  observer  a  strip  of 

239 


240        LABORATORY  EQUIPMENT  FOR 

black  paper  upon  a  white  background.  A  second  strip  of 
similar  paper  is  provided,  and  the  observer  is  required  by 
means  of  a  white  screen  to  cover  up  such  a  portion  of  this 
second  strip  as  he  may  desire,  and  to  place  the  visible  por- 
tion of  the  second  strip  across  the  first  piece  that  was  pro- 
vided. Here  again  lines  on  the  back  of  glass  may  be  used. 
For  the  third  part  of  the  experiment  a  series  of  figures 
cut  from  black  cardboard  or  from  colored  paper  may  be 
used  to  counterbalance  the  vertical  line  which  is  drawn 
upon  the  paper  at  the  outset  of  the  experiment.  These 
can  be  readily  adjusted  by  the  observer  until  he  is  satisfied. 
Measurements'  should  be  made  in  this  case  to  the  edge  of 
the  figure  which  is  nearest  to  the  central  point  in  the  field 
of  vision.  A  very  good  series  of  figures  for  this  purpose 
can  be  made  up  by  drawing  rectangles;  first,  five  which 
are  20  mm.  wide  and  successively  1,  2,  4,  8  cm.  long;  and, 
second,  five  which  are  each  4  cm.  long  and  successively 
1,  2,  3,  4  cm.  in  width.  Circles  of  various  sizes  are  also 
easily  produced. 

B — RESULTS 

The  formula  which  is  most  common  for  unequal  di- 
visions is  that  which  has  commonly  been  called  the  golden 
section  and  is  as  follows:  The  long  part  is  to  the  sum  of 
the  two  parts  as  the  short  part  is  to  the  long  part.  This 
principle  holds  also  for  the  division  of  crosses  and  for  the 
relation  between  their  two  legs. 

The  results  of  symmetrical  arrangement  of  figures  is 
a  matter  which  depends  on  the  size  of  the  figures.  Gen- 
erally speaking  a  large  figure  near  the  center  balances  a 
small  figure  far  away. 

C — SUPPLEMENTARY   EXPERIMENTS 

The  supplementary  experiments  require  no  comment, 
except  possibly  the  last,  which  refers  to  the  method  of 


PSYCHOLOGICAL  EXPERIMENTS        241 

selection.  This  method  consists  in  presenting  to  an  ob- 
server two  colors  or  forms,  and  asking  him  to  select  the 
one  which  is  more  agreeable.  Other  combinations  are 
now  presented,  including  the  selected  color  or  form,  until, 
finally,  by  a  succession  of  choices  the  observer  has  arrived 
at  a  final  selection  of  that  one  which  seems  to  him  to  be 
most  agreeable.  This  method  was  suggested  by  Fechner 
in  "Vorschule  der  Aesthetik." 


EXERCISE  XXV 

For  the  experiments  with  these  higher  mental  processes 
the  physical  conditions  are  not  elaborate.  The  appa- 
ratus may  be  of  the  simplest  sort.  In  the  two  experiments 
described,  the  apparatus  consisted  of  a  projection  lantern 
which  would  throw  images  upon  the  wall  in  front  of  the 
observer,  and  of  a  simple  light  which  could  be  turned  on 
the  wall  in  very  faint  intensities. 


242 


GENERAL  EQUIPMENT 


REQUIRED 


DESIRABLE 


Charts. 
Models. 


Drawing  material: 

Drawing  board. 

Drawing  paper. 

Thumb-tacks. 

T-square. 

Triangles. 

Ruling  pens. 

Compasses. 

India  ink. 
Carpenter's  tools. 

Electric  current. 


Table  clamps. 

S-clamps. 

Rods. 

Meter  rods,  tapes  and  rulers. 


Projection  lantern  with  slides. 
Photographic     equipment     for 

making  slides. 
Supply  of  millimeter  paper. 


Metal  and  wood-working  ma- 
chine shop. 

Lamp  batteries. 

Plugs  and  sockets  for  connec- 
tions. 


EXERCISE  I 


REQUIRED 

Sets  of  cards,  five  pairs  in  each 
set. 

Paper  on  which  to  mark  lengths 
of  lines  as  set. 

Holder  for  cards  during  adjust- 
ment. 

Millimeter  measure. 


DESIRABLE 


Apparatus  for  holding  cards 
with  recording  attachment 
and  roll  of  paper  on  which 
to  make  records. 

Thumb-tacks  to  fasten  cards  to 
boards. 


243 


244        LABORATORY  EQUIPMENT  FOR 
EXERCISE  II 

REQUIRED  DESIRABLE 

Head-rest     (table    clamps,        Head-rest  (independent). 

S-clamps,  rods.) 
Sealing-wax. 
Shield  for  eye. 
Colored  papers. 

Perimeter    or    campimeter    of        Perimeter    of    more    elaborate 
simple  construction.  type  with  light  box  for  ex- 

posure of  colors.  Electric 
connections. 

EXERCISE  III 

REQUIRED  DESIRABLE 

Colored  papers. 
Colored  disks. 

Simple  color  disk  rotator.  Electric  motor  with  arbor  for 

Protractor.  holding  disks.    (Current  con- 

nections, wires.) 

EXERCISE  IV 

REQUIRED  DESIRABLE 

Head -rest       (table       clamps,        Head-rest  (independent). 
S-clamps,  rods). 

Sealing-wax. 

Eye-shield. 

Meter  rod. 

Table  clamps,     S-clamps     and 
rods  to  hold  measuring  rod. 

Paper  ruled  in  large  squares. 

After-image  card.  Box  with  lamp  and  Aubert's  di- 

aphragm. Dark  room.  Elec- 
tric connections.  If  these  are 
not  at  hand  the  third  part  of 
the  exercise  must  be  omitted. 

EXERCISE  V 

REQUIRED  DESIRABLE 

Model  of  truncated  pyramid. 
Drawing  material: 
Paper,  ruler,  etc. 


PSYCHOLOGICAL  EXPERIMENTS        245 

REQUIRED  DESIRABLE 

Mirror   stereoscope    of   simple        Adjustable  mirror  stereoscope, 
construction. 

(Lens    stereoscope    may    be 
used.) 

EXERCISE  VI 

REQUIRED  DESIRABLE 

Head-rest  (clamps  on  chair).  Head-rest  (independent). 

Sealing-wax. 

Two  sounders.  Two  telephones,  mercury  key, 

electric  connections,  battery, 
wires. 

Interrupter. 

Auditory  cage,  simple  construe-        Auditory  cage,  adjustable, 
tion. 

EXERCISE  VII 

REQUIRED  DESIRABLE 

Quincke's  tubes. 

Mouthpiece  for  blowing  same 

in  combinations. 
Two  chromatic  pitch-pipes  with 

scale.  Set  of  tuning-forks. 

Resonators  (one  adjustable). 
Conducting  tubes  leading  from 
resonators. 

EXERCISE  VIII 

REQUIRED  DESIRABLE 

Stamp. 
Ink  pad. 

Metallic  points  in  cork.  Holder    for    various    kinds    of 

Wooden  rods,  sealing-wax,  bris-  points, 

ties  of  various  sizes.  Metallic  points. 

Bristles  and  grips  to  fit  holder. 

EXERCISE  IX 

REQUIRED  DESIRABLE 

Wooden  stylus. 
Aniline  ink. 

Compass  with  hard  rubber  or        Aesthesiometer  with  scales, 
bone  points. 


246        LABORATORY  EQUIPMENT  FOR 


REQUIRED 

Millimeter  measure. 
Pasteboards    cut    into    various 
lengths. 


DESIRABLE 


Hard  rubber  strips  with  edges  of 
various  lengths. 


Weights. 


EXERCISE  X 

REQUIRED  DESIRABLE 

Rotating  table  for  presentation 


Pith-ball  sounder  (simple  con- 
struction). 
Photometer  (shadow). 


of  weights  to  observer. 
Sounder  with  accurate  holder 
for  balls. 


EXERCISE  XI 


REQUIRED 

Tambour. 

Rubber  dam,  thread,  beeswax, 
rubber  tubing,  straws,  mate- 
rial for  points. 

Kymograph.  (If  no  motor  is 
provided  in  equipment,  clock- 
work kymograph). 

Kymograph  paper,  paste. 
Flame  for  smoking  paper. 
Shellac  tray  or  table. 
Electric  fork  with  connections. 


DESIRABLE 


REQUIRED 

Thistle  tube. 

Clamps  for  above. 

Rubber  tubing. 

Recording  tambour. 

Kymograph  and  accessories. 

Time  marker. 

Sugar  solution,  quinine  solution 


Air  valve. 


Two  drums. 

Pulleys    for    connection    with 

motor. 
Motor  and  connections. 


Marker  for  use  with  fork. 
Interrupter  for  longer  intervals. 
Pendulum    with    contacts    for 

long  intervals. 
Coarse  marker  recording  with 

ink  or  pencil. 
Jacquet  chronometer. 


EXERCISE  XII 

DESIRABLE 

Sphygmograph. 
Arm-rest. 


PSYCHOLOGICAL  EXPERIMENTS        247 
EXERCISE  XIII 

REQUIRED  DESIRABLE 

Tambours    (receiving   and   re- 
cording). 

Kymograph  and  accessories. 
Planchette  with  recording  pen. 

EXERCISE  XIV 

REQUIRED  DESIRABLE 

Spring  key  with  electric  connec- 
tions. 

Marker. 

Kymograph  and  accessories. 

Time  marker. 

Hand-rest  to  bring  the  reactor's        Apparatus    for    holding    paper 
hand  over  a  moving  paper  on  over  traveling  paper.    Type- 

which    he    may    draw    the  writer  ribbon  or  carbon  paper 

straight  lines  required.  underneath. 

EXERCISE  XV 

REQUIRED  DESIRABLE 

Two  keys  (experimenter's  and 

reactor's). 

Electric  tuning-fork  and  connec- 
tions. 

Ewald  chronoscope  and  wires 
for    connections,     or    Hipp 
chronoscope. 
Electric  markers. 

Tambours  (one  of  these  may  be        Lever  key  for  reaction  forms, 
substituted  for  the  reactor's        Sounder  to  give  signal, 
key).  Shutter  to  expose  colors. 

Kymograph  and  accessories. 

EXERCISE  XVI 

REQUIRED  DESIRABLE 

Three  keys  (experimenter's,  two 

for  reactor). 

Electric  fork  and  connections. 
Markers.  Chronoscope  and  connections. 


248        LABORATORY  EQUIPMENT  FOR 

REQUIRED  DESIRABLE 

Tambours.     (One  may  be  sub-  Lever  key  for  recording  form  of 

stituted  for  the  reactor's  key.)  reaction. 
Kymographs  and  accessories. 

Sounders. 

Color  exposure  apparatus  con-  Exposure  shutter. 

nected    with    experimenter's  Articulation  key. 

key. 

EXERCISE  XVII 

REQUIRED  DESIRABLE 

Attachment  for  kymograph  to 
take  record  of  writing.  Apparatus,  as  described  by  Mr. 

Recorder  to  attach  to  hand.  Freeman,  for  writing  record. 

Figure  for  moving  point  on  ky- 
mograph. 

Carbon  paper  to  record  hand        Cylinder    for    recording    band 
movements.  movements. 

EXERCISE  XVIII 

REQUIRED  DESIRABLE 

Series  of  patterns. 

Paper  for  drawing. 

Carbon  paper. 

Soft  paper. 

Metal  stylus. 

Millimeter  ruler. 

Protractor  to  measure  angles. 

EXERCISE  XIX 

REQUIRED  DESIRABLE 

Spring  key  with  connections. 

Marker. 

Time   marker  connected   with 

fork  or  interrupter. 
Kymograph  and  accessories. 
Figures. 

Watch.  Stop  watch. 

Cards  marked  with  numerals  or 

figures, 


PSYCHOLOGICAL  EXPERIMENTS        249 
EXERCISE  XX 

REQUIRED  DESIRABLE 

Spring   key   with    connections. 

Marker. 

Time-marker. 

Kymograph  and  accessories.  Porter's  ergograph. 

Metronome. 

EXERCISE  XXI 

REQUIRED  DESIRABLE 

Cards  with  nonsense  syllables. 

Kymograph  and  shield  for  ex- 
posure of  syllables. 

Ratchet  for  intermittent  move- 
ment of  kymograph. 

Wirth's  special  apparatus. 

EXERCISE  XXII 

REQUIRED  DESIRABLE 

Equivocal  figures. 

Key,  marker,  kymograph   and 

accessories,  time-marker. 
Stereoscope,  colored  papers. 
(Masson  disk,  color  mixer). 

EXERCISE  XXIII 

REQUIRED  DESIRABLE 

Metronome  and  shield.  Complication  pendulum. 

Exposure  apparatus  and  letters        Dodge's  exposure  apparatus. 

and  figures  for  same. 
Metronome  for  series  of  sounds.        Pendulum    with   contacts    and 

sounder,  or 

Spring  key,  marker,  kymograph        Attachment  for  Ludwig  Kymo- 
and  accessories.  graph  with  contacts  and  ham- 

mer. 

EXERCISE  XXIV 

REQUIRED  DESIRABLE 

Cards. 

Adjustable  lines.  Illusion    apparatus,    adjustable 

Millimeter  ruler.  cross-line  on  glass. 

Strips  of  black  paper. 

Black  card  figures  for  symmetry. 


LIST  OF  DEMONSTRATIONS 

TO  BE  USED  WITH  THE  AUTHOR'S  PSYCHOLOGY,  GENERAL  INTRO- 
DUCTION. THE  PAGE  REFERENCES  AT  THE  LEFT  ARE  TO  THAT 
VOLUME.  THE  PAGE  REFERENCES  AT  THE  RIGHT  ARE  TO  PAGES 
IN  THIS  VOLUME. 

PAGE  PAGE 

2.    Analyze  white  light  into  components  with  the  aid  of  a 

prism  or  spectroscope.    Or  mix  colors  and  produce  gray .     47 
6.     Memory  experiments  as  illustrating  method 222 

11.     Plotting  of  blind-spot 42 

15.    Chart  or  lantern  slide  of  amoeba  or  other  cells. 

17.    Other  charts  from  Jennings. 

23.  Models,  or  charts,  or  lantern  slides  of  nervous  system  of 
various  invertebrate  forms. 

27.  Preparation  or  model  of  frog's  nervous  system.  To  make 
the  preparation,  fine,  sharp-pointed  scissors,  a  scalpel, 
and  forceps  are  required.  The  frog  should  be  chloro- 
formed and  dissected. 

30.  Models  or  preparations  of  vertebrate  brains  higher  than 
frog. 

36.    Model  of  human  head  showing  brain  in  situ. 

36.  Model  of  brain  showing  sections.  (Azoux  brain  model  is 
the  best.) 

36.  Charts  or  slides  showing  various  types  of  cells  and  various 
parts  of  the  nervous  system  in  fine  anatomy. 

36.  Charts  by  Strumpell  and  Jakob,  published  by  J.  F.  Leh- 
mann,  Munich,  Germany. 

75.    Spectrum  (if  not  shown  in  connection  with  page  2). 

75.     Gray  and  colored  papers 36 

77.     Chart  of  color  circle. 

81.     Model  of  eye,  showing  parts. 

84.  Kiihne's  eye,  or  other  means  of  demonstrating  properties 
of  lenses  (camera  obscura). 

84.    Show  properties  of  monocular  image 64 

84.  Thread  model  showing  paths  of  rays  of  light  entering  the 
eye. 

84.     Model  showing  muscles  of  eye. 

250 


PSYCHOLOGICAL  EXPERIMENTS  251 

PAGE  PAGE 

89.  Charts  of  retina  when  dark-adapted  and  light-adapted. 

90.  Color-blindness,  normal  and  abnormal. 

93.     Color  mixing 47 

96.    Pigment  mixing 61 

96.  After-images 66 

97.  Color  contrasts 58 

103.     Appunn's   reed   to    demonstrate   origin   of   sound,  also 

lowest  tones 117 

103.  Galton's  whistle,  or  metal  bars  of  highest  tones 117 

104.  Records  of  sounds 106,  214 

105.  Model  of  ear,  showing  parts. 

109.     Experiments  on  bodily  localization 126 

113.     Beats  and  combination  tones  with  adjustable  forks  and 

Quincke's  tubes 106 

117.     Model  of  median  section  of  head. 
117.     Charts  of  sensory  surfaces. 

120.    Taste  experiments 120 

123.     Analysis  of  tactual  qualities 118 

125.    Model  of  skin,  showing  parts. 

128.    Weber's  Law.     (The  photometer  demonstration  is  best)  128 
131.    Functional  effects  of  sensations.     (Demonstration  better 
later.) 

138.    Tactual  space 121 

144.     Auditory   space.       (Simple  demonstration  with  snapper 

sounders)  98 

148.      Miiller-Lyer  and  other  illusions.      (Methods  of  meas- 
uring)   16 

154.     Retinal  image  and  objects 64 

157.     Binocular  depth 78 

160.     Stereograms  and  lens  stereoscopes 93 

160.  Monocular  flatness 68 

161.  Retinal  rivalry 86,  229 

175.     Time  experiments.     (Simple  series  of  taps  may  be  made 

by  the  instructor  to  test  the  range  of  recognition) ....  236 

184.  Dynamometer 214,  221 

185.  Sphygmograph,  or  plethysmograph 160 

186.  Planchette 169 

189.     Attention 220,  229,  231 

198.     Forms  of  simple  reactions 182 

205.     Aesthetics. .                                                                         .  239 


252        PSYCHOLOGICAL  EXPERIMENTS 

PAGE  PAGE 

206.  Illusion  of  weights 172 

209.  Tonal  fusions 113 

211.  Reproduction  of  tones 214 

219.  Diffusion  and  organization  of  habits 169,  217 

221.  Writing  and  other  coordinations 176,  206 

231.  Memory 224 

236.  Memory  in  broad  sense 213,  217 

317.  Throughout  this  chapter  see  Exercises  XII— XX. 

321.  Reflex  winking 219 

322.  Perceptual  activity 169 

323.  Form  of  action 192 

334.  Reaction  experiments 182 

358.  Aesthetical  appreciation 239 


INDEX 


PAGE 

Accommodation,  visual. .  .73, 84 

^Esthesiometer 122 

^Esthetic  appreciation 239 

After-image,  tactual 123 

After-image,  visual 66 

Air  pressure 107 

Air  valve 142 

Algometer 120 

Angell 199 

Apparatus,  lists  of 243 

Appunn Ill 

Arm  rest 162 

Articulation 214 

Articulation,  reactions 203 

Association,  free 204 

Association,  reactions 203 

Association,  restricted 204 

Attention 229 

Aubert's  diaphragm 66 

Audiometer,  telephone 129 

Auditory  cage 101 

Auditory  localization . . .  104, 105 

Balance,  aesthetic 240 

Batteries,  electric 4 

Battery,  lamp 6 

Beats 116 

Belt  kymograph 147 

Bergstrome 223, 226 

Binaural  perception 98 

Binocular  vision 78 

Blind-spot 42 

Bodily  localization 126 

Boekel  &  Co 109 

Brake  for  electric  motor ...  53 

Breese 95 

Brightness  contrast 58 

Brightness  equation 37 


PAGE 

Cage,  auditory 101 

Cameron 214 

Campimeter 35 

Capillary  pen 157 

Card-distribution  test 217 

Charts,  demonstration 2 

Charts,  visual  tests 76 

Chronoscope,  Ewald 183 

Chronoscope,  Hipp 187 

Chronometer,  Jaquet 153 

Circle  illusion 25 

Circular  measurements ....     15 

Circulatory  activities 160 

Clamps 9 

Color  absorption 61 

Color  blindness 41 

Color-blind  test 56 

Color  contrast 58 

Color  equations 56,  61 

Color  mixer 51,52,54 

Color  mixing 47 

Color  top 49 

Colored  papers 36 

Commutator 190 

Compass 121 

Complex  mental  processes..  242 
Complication  experiments. .  231 

Confusion  experiment 123 

Connection  for  Ewald  Chro- 
noscope     184 

Connection  for  Hipp  Chro- 
noscope     188 

Contact  apparatus 199 

Contrast,  brightness 58 

Contrast,  color 58 

Contrast  disks 59 

Control  hammer 190 

Convergence,  visual 88,  96 


253 


254 


INDEX 


Coordinate    aper 


PAGE 

nate  paper  .........  12 

Countershaft  .............  146 

Cutaneous  qualities  .......  118 

Cylinders  for  lowest  tones.  .  116 


Dark  adaptation  of  eye,  45,  46,  60 
Demonstrations  .........  1,  250 

Depth,  monocular  ........     71 

Depth,  perception  of  .....  68,  69 

Diaphragm,  Aubert's  ......     66 

Diedrich  .................   133 

Difference  tones  ..........   116 

Direction,    tactual    percep- 
tion of  ................   124 

Discrimination  reactions  .  .  .  203 
Disks,  color  ..............     49 

Distance,  auditory  ........     98 

Distance,  perception  of  ....     72 

Distraction  ..............  220 

Division,  aesthetical  .......  239 

Dodge  ..................  234 

Double  images  ...........     78 

Drawing  .................       3 

Drawing  reaction  ......  175,  213 

Dynamometer  ............   172 

Edelmann  ...............  117 

Edison-Lalande  batteries  .  .  4 

Electric  motor  ............  52 

Electric  plug  .............  7 

Electrical  connections  .....  3 

Equation  for  retinal  image.  65 

Equivocal  figures  .........  229 

Exposure  apparatus.  ...  196,  234 

Exposure  shutter  .........  198 

Eye  shield  ...............  31 

Fall  apparatus,  sound.  .  129,  132 
Fall  tachistoscope  .........   197 

Fatigue  ..................  221 

Fechner  .................  241 

Filled  space  illusion  .......     26 

Fluctuation  of  attention.  .  .  .  229 

Form  of  reaction  ..........   192 

Freeman  .........  176,  180,206 


PACK 

Friction  clutch 177 

Fusion,  tonal 115 

Galton's  whistle 117 

Gelatine 40 

Golden  section 240 

Graphic  representations ...  12 

Gray  paper 44 

Habit 217 

Hammer,  electric 189 

Hand  movement  recorder.  .  211 

Hathaway 2 

Head  rest 31 

Helmholtz'    rotation   appa- 
ratus  146, 236 

Henderson 166 

Henri 124 

Hering 36 

Illusion  apparatus 18,  28 

Illusion  of  weights 172 

Illusion,  visual 16 

Initial  threshold 11,  128 

Interrupter,  electric 99 

Interrupter,  Kronecker.  .  .  .   156 

Introduction 1 

Inverted  shadows 70 

Involuntary  movements.  160, 169 

Jaquet  chronometer 153 

Jastrow 171 

Keyboard,  organ 109 

Kinetoscope 88 

Kohl 87,  110 

Kronecker,  interrupter 156 

Kymograph 143 

Kymograph  record 158 

Lamp  battery 4 

Lampblack 150 

Lantern,  for  demonstrations,      2 

Laryngograph 171 

Light  adaptation  of  eye. ...     45 


INDEX 


255 


PAGE 

Light-box,  for  perimeter ...     39 

Light  contrasts 58 

Lines,  tactual  perception  of,  124 

Localization,  auditory 104 

Localization,  bodily 126 

Localization,  tactual 121 

Loomis 174 

Lowest  tones 116,  117 

Ludwig  kymograph ....  145,  236 

Marbe.. 54 

Marker,  electric 155 

Marking-out  test 204 

Masson  disk 230 

Memory 234 

Mercury  contacts 157 

Metronome 220,  231 

Meyrowitz 38,  39 

Milton-Bradley 37,  51 

Minimum  visibile 75 

Mirrors,  single  image 84 

Mixer,  color 51,  52,  54 

Models,  demonstration ....       2 

Monochord 228 

Monocular  adjustments. ...   175 

Monocular  depth 73 

Monocular  vision 64,  68,  86 

Mosso's  ergograph 221 

Motor,  electric 52 

Movement,  tactual  percep- 
tion of 125 

Miiller-Lyer  illusion .  .  12,  16,  22 
Miinsterberg 51 

Nonsense  syllables 224 

Odors 133 

Olfactometer 133 

Organ  pipes 109 

Pain 120 

Paper-cutter  for  disks 50 

Pen,  universal 170 

Pencil  marker 157 

Pendulum,  complication .  . .  231 


PAGE 

Pendulum,  contact 226,  236 

Pendulum,  sound 133 

Perimeter 33 

Peripheral  vision 34,  41,  45 

Peripheral  vision  of  form .  .     44 

Personal  equation 237 

Personal  factor  in   experi- 
ments      11 

Photometer 131 

Photometry 45 

Pierce 105,233 

Pigment  mixtures 61 

Pillsbury 124 

Pifch-pipe,  chromatic 106 

Pith-ball  audiometer 129 

Planchette 169 

Plethysmograph 164 

Plug  contact 7 

Pneumograph 167 

Poggendorff  illusion 24 

Porter 137 

Porter's  ergograph 222 

Porter's  kymograph 144 

Practice  curve 13,  14 

Practice  results 217 

Practice  tests 217 

Preface i 

Pressure  recorder 178 

Pressure  spots 119 

Pressure  threshold 135 

Procedure  with  knowledge.     10 
Procedure   without   knowl- 
edge      10 

Projection,  visual 64 

Protractor 50 

Pseudoptics 51 

Pseudoscope 91 

Psychology,  General  Intro- 
duction  1,  14,80,  171 

Pupilar  reaction 168 

Quincke's  tubes , 106 

Reactions,  complex 201 

Reactions,  simple 182 


256 


INDEX 


Reaction  key 193 

Reaction,  writing 206,  208 

Recording  points 141 

Recording  tambour 138 

Reflex  winking 219 

Relativity,  temperature ....   119 

Resonators 113 

Retinal  image 65 

Retinal  rivalry 86,  95,  230 

Rotating  table 127 

Rothe 36,52 

Rousselot 171,  172 

Sanford 191 

Scripture 4,  191 

Scripture's  touch  key 199 

Seashore 103 

Section,  golden 240 

Semicircular  canals 126 

Sensation,  intensities  of. ...   128 

Shellac  bottle 151 

Shellac  tray 150 

Schumann 236 

Size,  visual  perception  of .  .66, 71 

Smith,  C.  H iii 

Snapper  sounder 98 

Socket,  electric 8 

Solar  prints 2 

Solidity 80,87 

Sonometer Ill 

Sound  hammer 189 

Sound  pendulum 133 

Sound  threshold 128 

Spectroscope 37 

Spectrum 47 

Sphygmograph 160 

Sprague 2 

Spring  key  for  tapping 175 

Stamp  for  skin 118 

Standard 159 

Standard  Dictionary 38 

Stereograms 81,  94 

Stereoscope,  lens 92 

Stereoscope,  mirror 82 


Stereoscope,  Wheatstone ...       9 

Stern Ill 

Stern's  tone-variator 134 

Stocking  Co 36,  37,  44,  99, 

111,138,153,220,221,222 

Stratton 91 

Stroboscope 87 

Stumpf 116 

Symmetry  of  figures 239 

Table-clamp 9 

Tactual  localization 121 

Tactual  threshold 125 

Tambour 137 

Tambour  pen 212 

Tapping 175,  181,220 

Target  experiment 215 

Taste 120,  134 

Teeth-rest 33 

Teeuwen iii 

Telestereoscope 92 

Temperature  spots 118 

Thistle-tube  sphygmograph,  160 

Threshold,  initial 11,  128 

Threshold,  pressure 135 

Threshold,  sound 128 

Threshold,  tactual 125 

Time,  empty 238 

Time  experiments 236 

Time,  filled 238 

Titchener 108 

Tonal  fusion 115 

Tonal  intervals 115,  116 

Tonal  perception 106 

Tone  conductors 112 

Tone-messer Ill 

Tone-variator Ill 

Tongue  bulbs 172 

Tuning-fork 112 

Tuning-fork,  electric 153 

Tuning-fork  holder 155 

Typewriter  test 219 

Underwood  &  Underwood .     94 


INDEX 


257 


Valve,  air-pressure 109 

Vaso-motor  reactions 164 

Verdin 140,  171 

Vision,  acuity  of 76 

Vision,  binocular 78 

Vision,  chart  tests 76 

Vision,  monocular 64 

Visual  distance 66 

Voice  key 201 

von  Frey 122 

Watch  test  for  ear 130 

Weber's  Law 128 

Weight  illusion 173 

Weights,      psycho-physical 
tests.  .  .  .128 


PAGE 

Wheatstone  stereoscope 9 

Whipple 108,205 

Whisper  test  for  ear 130 

Winking  reflex 219 

Wirth 227 

Witmer 58 

Writing  reactions 206 

Writing  recorder 177 

Wundt 112,  113,  132,  185, 

186,  201,  231,  232 


Zimmermann 135,  144,  145, 

146,  156,  165,  189,  190,  225, 
226 

Zollner  illusion . .  27 


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*™  1  7  ,94, 

CWjl  ;,T  03Q 

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i          OCT    92  1Q47 

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|              w- 

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JMIM  2  4    1954 

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JUN  2  8  1960 

JUN231960 

IAII  1  R  1962 

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cr  7  'fior  i 

LD  21-100jn-8,'34 

&IOLOG7  LIBiUKf 


